Download Oscilloscope HM 303-4 GB

Table of contents
Oscilloscope datasheet
St. 170698/hüb/goRR
Operating Instructions
Symbols ............................................................
General Information ...........................................
Use of tilt handle ...............................................
Safety ................................................................
Operating conditions .........................................
Warranty ............................................................
Maintenance .....................................................
Protective Switch-Off ........................................
Power supply ....................................................
Type of signal voltage ........................................
Amplitude Measurements .................................
Time Measurements .........................................
Connection of Test Signal .................................
First Time Operation ..........................................
Trace Rotation TR ..............................................
Probe compensation and use ............................
Operating Modes of the Y Amplifier .................
X-Y Operation ....................................................
Phase difference measurement
in DUAL mode ............................................
Measurement of an amplitude modulation .......
Triggering and Timebase ...................................
Automatic Triggering .........................................
Normal Triggering, Slope ...................................
Trigger Coupling ................................................
Triggering of Video Signals ................................
Line Triggering ...................................................
Alternate Triggering ...........................................
External Triggering ............................................
Trigger Indicator ................................................
Function of variable HOLD OFF control .............
Y Overscanning Operation ................................
Component Tester ............................................
Test Patterns .....................................................
Test Instructions
General ..............................................................
Cathode-Ray Tube: Brightness, Focus,
Linearity, Raster Distortions .........
Astigmatism Check ...........................................
Symmetry and Drift of the Vertical Amplifier ....
Calibration of the Vertical Amplifier ...................
Transmission Performance
of the Vertical Amplifier .................................
Subject to change without notice
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Oscilloscope
GB HM 303-4
Operating Modes:CHI/II-TRIG.I/II, DUAL, ADD,
CHOP., INV.I/II and XY-Operation .................
Triggering Checks ..............................................
Timebase ...........................................................
Component Tester ............................................
Trace Alignment ................................................
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Service Instructions
General ..............................................................
Instrument Case Removal .................................
Operating Voltages ............................................
Maximum and Minimum Brightness .................
Astigmatism control ..........................................
Trigger Threshold ..............................................
Trouble-Shooting the Instrument .......................
Replacement of Components and Parts ...........
Adjustments ......................................................
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Short Instruction . ...............................................
Front Panel Elements, Front View . ..................
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1
General information regarding the CE marking
HAMEG instruments fulfill the regulations of the EMC directive. The conformity test made by
HAMEG is based on the actual generic- and product standards. In cases where different limit
values are applicable, HAMEG applies the severer standard. For emission the limits for residential,
commercial and light industry are applied. Regarding the immunity (susceptibility) the limits for
industrial environment have been used.
The measuring- and data lines of the instrument have much influence on emmission and immunity
and therefore on meeting the acceptance limits. For different applications the lines and/or cables
used may be different. For measurement operation the following hints and conditions regarding
emission and immunity should be observed:
1. Data cables
For the connection between instruments resp. their interfaces and external devices, (computer,
printer etc.) sufficiently screened cables must be used. Without a special instruction in the manual
for a reduced cable length, the maximum cable length of a dataline must be less than 3 meters
long. If an interface has several connectors only one connector must have a connection to a cable.
Basically interconnections must have a double screening. For IEEE-bus purposes the double screened
cables HZ72S and HZ72L from HAMEG are suitable.
2. Signal cables
Basically test leads for signal interconnection between test point and instrument should be as
short as possible. Without instruction in the manual for a shorter length, signal lines must be less
than 3 meters long.
Signal lines must screened (coaxial cable - RG58/U). A proper ground connection is required. In
combination with signal generators double screened cables (RG223/U, RG214/U) must be used.
3. Influence on measuring instruments.
Under the presence of strong high frequency electric or magnetic fields, even with careful setup of
the measuring equipment an influence of such signals is unavoidable.
This will not cause damage or put the instrument out of operation. Small deviations of the measuring
value (reading) exceeding the instruments specifications may result from such conditions in individual
cases.
December 1995
HAMEG GmbH
KONFORMITÄTSERKLÄRUNG
DECLARATION OF CONFORMITY
DECLARATION DE CONFORMITE
Name und Adresse des Herstellers
Manufacturer´s name and address
Nom et adresse du fabricant
®
Instruments
HAMEG GmbH
Kelsterbacherstraße 15-19
D - 60528 Frankfurt
HAMEG S.a.r.l.
5, av de la République
F - 94800 Villejuif
Die HAMEG GmbH / HAMEG S.a.r.l bescheinigt die Konformität für das Produkt
The HAMEG GmbH / HAMEG S.a.r.l herewith declares conformity of the product
HAMEG GmbH / HAMEG S.a.r.l déclare la conformite du produit
Bezeichnung / Product name / Designation: Oszilloskop/Oscilloscope/Oscilloscope
Typ / Type / Type:
HM303-4
mit / with / avec:
-
Optionen / Options / Options:
-
mit den folgenden Bestimmungen / with applicable regulations / avec les directives suivantes
EMV Richtlinie 89/336/EWG ergänzt durch 91/263/EWG, 92/31/EWG
EMC Directive 89/336/EEC amended by 91/263/EWG, 92/31/EEC
Directive EMC 89/336/CEE amendée par 91/263/EWG, 92/31/CEE
Niederspannungsrichtlinie 73/23/EWG ergänzt durch 93/68/EWG
Low-Voltage Equipment Directive 73/23/EEC amended by 93/68/EEC
Directive des equipements basse tension 73/23/CEE amendée par 93/68/CEE
Angewendete harmonisierte Normen / Harmonized standards applied / Normes harmonisées utilisées
Sicherheit / Safety / Sécurité
EN 61010-1: 1993 / IEC (CEI) 1010-1: 1990 A 1: 1992 / VDE 0411: 1994
Überspannungskategorie / Overvoltage category / Catégorie de surtension: II
Verschmutzungsgrad / Degree of pollution / Degré de pollution: 2
Elektromagnetische Verträglichkeit / Electromagnetic compatibility / Compatibilité électromagnétique
EN 50082-2: 1995 / VDE 0839 T82-2
ENV 50140: 1993 / IEC (CEI) 1004-4-3: 1995 / VDE 0847 T3
ENV 50141: 1993 / IEC (CEI) 1000-4-6 / VDE 0843 / 6
EN 61000-4-2: 1995 / IEC (CEI) 1000-4-2: 1995 / VDE 0847 T4-2:
Prüfschärfe / Level / Niveau = 2
EN 61000-4-4: 1995 / IEC (CEI) 1000-4-4: 1995 / VDE 0847 T4-4:
Prüfschärfe / Level / Niveau = 3
EN 50081-1: 1992 / EN 55011: 1991 / CISPR11: 1991 / VDE0875 T11: 1992
Gruppe / group / groupe = 1, Klasse / Class / Classe = B
Datum /Date /Date
14.12.1995
Unterschrift / Signature /Signatur
.
Dr. J. Herzog
Technical Manager
Directeur Technique
.
OSCILLOSCOPES
Specifications
Vertical Deflection
Operating modes: Channel I or II separate,
both Channels (alternated or chopped),
(Chopper frequency approx. 0.5MHz).
Sum or difference with Ch. I and Ch. II
(both channels invertable).
XY-Mode: via channel I and channel II
Frequency range: 2xDC to 30MHz (−3dB)
Risetime: <12ns.
Overshoot ≤1%.
Deflection coefficients: 12 calibrated steps
from 5mV/div. to 20V/div. (1-2-5 sequence)
with variable 2.5:1 up to 50V/div.
Accuracy in calibrated position: ±3%
Y-expansion x5 (calibrated) to 1mV/div. (±5%)
in the frequency range from DC - 10MHz (–3dB)
Input impedance: 1MΩ II 20pF.
Input coupling: DC-AC-GD (ground).
Input voltage: max. 400V (DC + peak AC).
Triggering
Automatic: (peak to peak) <20Hz-100MHz (≤ 0.5div.)
Normal with level control: DC-100MHz (≤0.5div.)
ALT. Triggering; LED indicator for trigger action
Slope: positive or negative,
Sources: Channel I or II, CH. I alternating CH II,
line, external
Coupling: AC (10Hz to 100MHz),
DC (0 to 100MHz),
LF (0 to 1.5kHz)
Active TV-Sync-Separator (pos. and neg.)
External: ≥0.3Vp-p from 30Hz to 30MHz
Horizontal Deflection
Time coefficients: 20 calibrated steps
from 0.2s/div. - 0.1µs/div. in 1-2-5 sequence
Accuracy in calibrated position: ±3%.
Min. speed incl. variable 2.5:1: 0.5s/div.
with X-Mag. x10: ±5%; 10ns/div.: ±8%
Holdoff time: variable to approx. 10:1
Bandwidth X-amplifier: 0-3MHz (−3dB).
Input X-Amplifier via Channel II,
(sensitivity see Channel II specification)
X-Y phase shift: <3° below 220kHz.
Component Tester
Test voltage: approx. 6Vrms (open circuit).
Test current: approx. 5mArms (shorted).
Test frequency: approx. 50Hz
Test connection: 2 banana jacks 4mm ∅
One test lead is grounded (Safety Earth)
General Information
CRT: D14-364GY/123 or ER151-GH/-,
6" rectangular screen (8x10cm)
internal graticule
Acceleration voltage: approx 2000V
Trace rotation: adjustable on front panel
Calibrator: square-wave generator (tr <4ns)
≈1kHz / 1MHz; Output: 0.2V ±1% and 2V
Line voltage: 100-240V AC ±10%, 50/60Hz
Power consumption: approx. 36 Watt at 50Hz.
Min./Max. ambient temperature: −10°C...+40°C
Protective system: Safety class I (IEC 1010-1)
Weight: approx. 5.6kg, color: techno-brown
Cabinet: W 285, H 125, D 380 mm
Lockable tilt handle
Subject to change without notice.
3/95
30MHz Standard Oscilloscope HM 303
Dual Channel, DC to 30MHz, 1mV/div.; Overscan Indicator
Time Base: 0.5s to 10ns/div.; Variable Holdoff; Alternate Triggering
Triggering: DC-100MHz; Auto Peak to Peak; Active TV-Sync-Separator
Additional Features: Component Tester, 1kHz/1MHz Calibrator
The new HAMEG HM303 oscilloscope succeeds the HM203 (over 170,000
sold worldwide). The bandwidth has been extended from 20 to 30MHz, the sweep
rate increased to 10ns/div. and improvements added to the already legendary
HAMEG auto triggering system. The HM303 is the ideal instrument for waveform
display in the DC to 70MHz frequency range.
A key feature of this oscilloscope is the vertical amplifier's pulse fidelity, limiting
overshoot to only 1%. The HM303 offers a special fast rise time, 1kHz/1MHz
Calibrator permitting high quality probe compensation across the entire frequency
range to ensure probe-tip thru to display integrity. An Overscan Indicator assists
in vertical display amplitude and position adjustment.
The HM303 is capable of triggering on input waveforms over 100MHz and on
signal levels as small as 0.5 division. Alternate triggering mode enables the
display of two asynchronous signals simultaneously. An active Video SyncSeparator permits detailed examination of complex TV signal inputs. A well
proven, built-in component tester is now equipped with a stabilized measuring
voltage. The use of a switching type of power supply minimizes both weight and
power consumption and universally accepts a wide range of input power line
voltages, without the requirement to change jumpers or switch positions. The
HM303's CRT is fully mu-metal shielded against outside magnetic fields.
HAMEG is setting newprice/performance breakthroughs with the introduction
of this fine oscilloscope. This performance packed scope will tempt all users to run
it through its paces.
Screen photo of 1 MHz square wave signal
Screen photo of 50 and 100MHz
sine wave with alternate triggering
Accessories supplied: Line cord, Operators Manual, 2 Probes 1:1/10:1
OSCILLOSCOPES
HZ 56 AC/DC Current Probe
Utilising Hall Effect technology to provide a broad frequency response, the
probe will accurately measure AC, DC and complex waveforms. The compact
clip-on design conforms to the IEC1010 safety standard and allows nonintrusive measurement of current from 5mA to 30A peak to an accuracy of
±1%. The probe gives a voltage output directly proportional to the measured
current which is compatible with a wide range of measuring instruments.
Specifications:
Current range:
Accuracy:
Dielectric strength:
Output sensitivity:
20A DC / 30A AC
± 1% ± 2mA
3.7kV, 50Hz, 1min.
100mV/A
Frequency range:
Resolution:
Load impedance:
Divers:
DC-100kHz
±1mA
>100kΩ
BNC-cable, 2m.
HZ 72/S/L
HZ36
Accessories
supplied
HZ38
HZ51
HZ 34S
HZ52
HZ20
HZ 32
HZ22
HZ 33
HZ53
HZ23
HZ54
HZ 33W
HZ24
HZ84-2
HZ20
HZ22
HZ23
HZ24
HZ58
Adaptor BNC to 4mm binding posts
50Ω BNC Feed-through termination 1GHz, 1W
Attenuator 2:1, BNC male to BNC female, for oscilloscope service only.
Set of 4 BNC 50Ω attenuators; 3/6/10/20dB; 1GHz, 1W, incl. 1x HZ22
HZ39 Spare Cable for HZ36
HZ57 Spare Cable for HZ51, HZ54
Spare-parts for modular probes only
Spare-part Kit HZ40
Test Cables
HZ32
HZ33
HZ33S
HZ33W
HZ34
HZ34S
HZ72S
HZ72L
HZ84-2
HZ84-3
Test cable BNC to single stacking banana plugs; 40 inch
Coaxial cable BNC/BNC, 50Ω, 20 inch
Coaxial cable BNC/BNC, 50Ω, 20 inch, insulated
Coaxial cable BNC/BNC, 50Ω, 20 inch, elbow
Coaxial cable BNC/BNC, 50Ω, 40 inch
Coaxial cable BNC/BNC, 50Ω, 40 inch, insulated
IEEE-488-Bus-Cable, 40 inch. double shielded
IEEE-488-Bus-Cable, 60 inch, double shielded
Spare Printer Cable for HD148 (CE) and HM305 / 1007 (CE)
Spare Printer Cable for combination of 25pole D-SUB / 26pole plastic male
Wide Band Probes with RF alignment
Type
HZ36
HZ51
HZ52
HZ53
HZ54
Attenuation
Max.
Bandwidth Risetime Input Impedance
Ratio
Input Voltage
1:1/10:1
10/100MHz <35/3.5ns 1/10MΩII57/12pF (10:1) 600V (DC+peak AC)
10:1
150MHz
<2.4ns
10MΩII12pF
600V (DC+peak AC)
10:1
250MHz
<1.4ns
10MΩII10pF
600V (DC+peak AC)
100:1
100MHz
<3.5ns
100MΩII4.5pF
1200V (DC+peak AC)
1:1/10:1
10/150MHz <35/2.4ns 1/10MΩII57/12pF (10:1) 600V (DC+peak AC)
Special Probes
HZ38 Demodulator Probe 0.1 - 500MHz
HZ58 High Voltage Probe, 1000:1; Ri approx. 500MΩ; DC - 1MHz
max. 200V (DC)
max. 15kV (DC+peak AC)
HZ47 Viewing Hood for Oscilloscopes HM205, 408, 604-1+2, 1005 and 1007
HZ48 Viewing Hood for Oscilloscopes 303, 304, 305, 604-3 and 1004
HZ40
HZ39
HZ57
HZ96 Carrying Case
for oscilloscopes HM203, 205, 208,
408, 604, 1005 and 1007
HZ97 Carrying Case for HM303, 304,
305, 604-3, 1004 and HM5005 / 6 / 10.
The carrying case provides protection
during transportation of an oscilloscope. It is made
of a durable vinylcoated material
that is designed to
withstand the
stress and wear
and tear of field
use.
Subject to change without notice
05/96
Operating Instructions
Symbols
Safety
See user's manual
Danger high voltage
Earth
General Information
This oscilloscope is easy to operate. The logical
arrangement of the controls allows anyone to quickly
become familiar with the operation of the instrument,
however, experienced users are also advised to read
through these instructions so that all functions are
understood.
Immediately after unpacking, the instrument should be
checked for mechanical damage and loose parts in the
interior. If there is transport damage, the supplier must be
informed immediately. The instrument must then not be
put into operation.
Use of tilt handle
To view the screen from the best angle, there are three
different positions (C, D, E) for setting up the instrument. If
the instrument is set down on the floor after being carried,
the handle automatically remains in the upright carrying
position (A).
In order to place the instrument onto a horizontal surface, the
handle should be turned to the upper side of the oscilloscope
(C). For the D position (10° inclination), the handle should be
turned to the opposite direction of the carrying position until
it locks in place automaticallyunderneath the instrument. For
the E position (20° inclination),the handle should be pulled to
release it from the D position and swing backwards until it
locks once more.
The handle may also be set to a position for horizontal
carrying by turning it to the upper side to lock in the B
position. At the same time, the instrument must be lifted,
because otherwise the handle will jump back.
This instrument has been designed and tested in accordance with IEC Publication 348, Safety Requirements
for Electronic Measuring Apparatus. The CENELEC
HD401 regulations correspond to this standard. It has left
the factory in a safe condition. This instruction manual
contains important information and warnings which have
to be followed by the user to ensure safe operation and to
retain the oscilloscope in a safe condition. The case,
chassis and all measuring terminals are connected to the
protective earth contact of the appliance inlet. The
instrument operates according to Safety Class I (threeconductor power cord with protective earthing conductor
and a plug with earthing contact). The mains/line plug shall
only be inserted in a socket outlet provided with a protective
earth contact. The protective action must not be negated
by the use of an extension cord without a protective
conductor.
The mains/line plug should be inserted before connections
are made to measuring circuits.
The grounded accessible metal parts (case, sockets,
jacks) and the mains/line supply contacts (line/live, neutral) of the instrument have been tested against insulation
breakdown with 2200V DC.
Under certain conditions, 50Hz or 60Hz hum voltages
can occur in the measuring circuit due to the interconnection with other mains/line powered equipment
or instruments. This can be avoided by using an isolation
transformer (Safety Class II) between the mains/line
outlet and the power plug of the device being
investigated.
Most cathode-ray tubes develop X-rays. However, the
dose equivalent rate falls far below the maximum
permissible value of 36pA/kg (0.5mR/h).
Whenever it is likely that protection has been impaired,
the instrument shall be made inoperative and be secured
against any unintended operation. The protection is likely
to be impaired if, for example, the instrument
− shows visible damage,
− fails to perform the intended measurements,
− has been subjected to prolonged storage under
unfavourable conditions (e.g. in the open or in moist
environments),
− has been subject to severe transport stress (e.g. in poor
packaging).
6
Subject to change without notice
Operating conditions
The instrument has been designed for indoor use. The
permissible ambient temperature range during operation
is +10°C (+50°F) ... +40°C (+104°F). It may occasionally be
subjected to temperatures between +10°C (+50°F) and 10°C (+14°F) without degrading its safety. The permissible
ambient temperature range for storage or transportation is
-40°C (-40°F) ... +70°C (+158°F). The maximum operating
altitude is up to 2200m (non-operating 15000m). The
maximum relative humidity is up to 80%. If condensed
water exists in the instrument it should be acclimatized
before switching on. In some cases (e.g. extremely cold
oscilloscope) two hours should be allowed before the
instrument is put into operation. The instrument should be
kept in a clean and dry room and must not be operated in
explosive, corrosive, dusty, or moist environments. The
oscilloscope can be operated in any position, but the
convection cooling must not be impaired. The ventilation
holes may not be covered. For continuous operation the
instrument should be used in the horizontal position,
preferably tilted upwards, resting on the tilt handle.
The specifications stating tolerances are only valid if
the instrument has warmed up for 30 minutes at an
ambient temperature between +15°C (+59°F) and
+30°C (+86°F). Values without tolerances are typical
for an average instrument.
Warranty
HAMEG warrants to its Customers that the products it
manufactures and sells will be free from defects in materials
and workmaship for a period of 2 years. This warranty
shall not apply to any defect, failure or damage caused by
improper use or inadequate maintenance and care. HAMEG
shall not obliged to provide service under this warranty to
repair damage resulting from attempts by personnel other
than HAMEG represantatives to install, repair, service or
modify these products. In order to obtain service under this
warranty, Customers must contact and notify the distributor
who has sold the product. Each instrument is subjected to
a quality test with 10 hour burn-in before leaving the
production. Practically all early failures are detected by this
method. In the case of shipments by post, rail or carrier it
is recommended that the original packing is carefully
preserved. Transport damages and damage due to gross
negligence are not covered by the guarantee. In the case of
a complaint, a label should be attached to the housing of the
instrument which describes briefly the faults observed. If at
the same time the name and telephone number (dialing
code and telephone or direct number or department
designation) is stated for possible queries, this helps towards
speeding up the processing of guarantee claims.
Maintenance
Various important properties of the oscilloscope should be
carefully checked at certain intervals. Only in this way is
it largely certain that all signals are displayed with the
accuracy on which the technical data are based. The test
methods described in the test plan of this manual can be
Subject to change without notice
performed without great expenditure on measuring
instruments. However, purchase of the new HAMEG
scope tester HZ 60, which despite its low price is highly
suitable for tasks of this type, is very much recommended.
The exterior of the oscilloscope should be cleaned
regularly with a dusting brush. Dirt which is difficult to
remove on the casing and handle, the plastic and
aluminium parts, can be removed with a moistened
cloth (99% water +1% mild detergent). Spirit or washing benzine (petroleum ether) can be used to remove
greasy dirt. The screen may be cleaned with water or
washing benzine (but not with spirit (alcohol) or solvents),
it must then be wiped with a dry clean lint-free cloth.
Under no circumstances may the cleaning fluid get into
the instrument. The use of other cleaning agents can
attack the plastic and paint surfaces.
Protective Switch-Off
This instrument is equipped with a switch mode power
supply. It has both overvoltage and overload protection,
which will cause the switch mode supply to limit power
consumption to a minimum. In this case a ticking noise
may be heard.
Power supply
The oscilloscope operates on mains/line voltages between
100VAC and 240VAC. No means of switching to different
input voltages has therefore been provided. The power
input fuses are externally accessible. The fuseholder is
located above the 3-pole power connector. The power
input fuses are externally accessible, if the rubber conector
is removed. The fuseholder can be released by pressing
its plastic retainers with the aid of a small screwdriver. The
retainers are located on the right and left side of the holder
and must be pressed towards the center. The fuse(s) can
then be replaced and pressed in until locked on both sides.
Use of patched fuses or short-circuiting of the fuseholder
is not permissible; HAMEG assumes no liability whatsoever
for any damage caused as a result, and all warranty claims
become null and void.
Fuse type:
Size 5x20mm; 0.8A, 250V AC fuse;
must meet IEC specification 127,
Sheet III (or DIN 41 662
or DIN 41 571, sheet 3).
Time characteristic: time-lag.
Attention!
There is a fuse located inside the instrument within
the switch mode power supply:
Size 5x20mm; 0.5A, 250V AC fuse;
must meet IEC specification 127,
Sheet III (or DIN 41 662
or DIN 41 571, sheet 3).
Time characteristic: fast (F).
This fuse must not be replaced by the operator!
7
Type of signal voltage
With the HM 303, most repetitive signals in the frequency
range up to at least 30MHz (−3dB) can be examined.
Sinewave signals of 50MHz are displayed with a height of
approx. 50% (−6dB). However when examining square or
pulse type waveforms, attention must be paid to the
harmonic content of such signals. The repetition
frequency (fundamental frequency) of the signal must
therefore be significantly smaller than the upper limit
frequency of the vertical amplifier.
Displaying composite signals can be difficult, especially if
they contain no repetive higher amplitude content which
can be used for triggering. This is the case with bursts, for
instance. To obtain a well-triggered display in this case,
the assistance of the variable holdoff and/or variable
time control may be required. Television video signals
are relatively easy to trigger using the built-in TV-SyncSeparator (TV).
For optional operation as a DC or AC voltage amplifier, the
vertical amplifier input is provided with a DC/AC switch.
The DC position should only be used with a seriesconnected attenuator probe or at very low frequencies or
if the measurement of the DC voltage content of the signal
is absolutely necessary.
When displaying very low frequency pulses, the flat tops
may be sloping with AC coupling of the vertical amplifier
(AC limit frequency approx. 1.6 Hz for 3dB). In this case,
DC operation is preferred, provided the signal voltage is
not superimposed on a too high DC level. Otherwise a
capacitor of adequate capacitance must be connected to
the input of the vertical amplifier with DC coupling. This
capacitor must have a sufficiently high breakdown voltage
rating. DC coupling is also recommended for the display
of logic and pulse signals, especially if the pulse duty
factor changes constantly. Otherwise the display will
move upwards or downwards at each change. Pure direct
voltages can only be measured with DC-coupling.
difference in Vpp. The relationship between the different
voltage magnitudes can be seen from the following figure.
Vp
Vrms
Vmom
Vpp
Voltage values of a sine curve
Vrms = effective value; Vp = simple peak or crest value;
Vpp = peak-to-peak value; Vmom = momentary value.
The minimum signal voltage which must be applied to the
Y input for a trace of 1div. height is 1mVpp when the YMAG. x5 pushbutton is depressed, the VOLTS/DIV.
switch is set to 5mV/div., and the vernier is set to CAL by
turning the fine adjustment knob of the VOLTS/DIV.
switch fully clockwise. However, smaller signals than this
may also be displayed. The deflection coefficients on
the input attenuators are indicated in mV/div. or V/div.
(peak-to-peak value).
The magnitude of the applied voltage is ascertained
by multiplying the selected deflection coefficient by
the vertical display height in div.
If an attenuator probe x10 is used, a further
multiplication by a factor of 10 is required to ascertain
the correct voltage value.
For exact amplitude measurements, the variable control
on the attenuator switch must be set to its calibrated
detent CAL. When turning the variable control ccw, the
sensitivity will be reduced by a factor of 2.5.
Therefore every intermediate value is possible within
the 1-2-5 sequence.
With direct connection to the vertical input, signals up to
400Vpp may be displayed (attenuator set to 20V/div.,
variable control to left stop).
Amplitude Measurements
With the designations
In general electrical engineering, alternating voltage data
normally refers to effective values (rms = root-meansquare value). However, for signal magnitudes and voltage
designations in oscilloscope measurements, the peak-topeak voltage (Vpp) value is applied. The latter corresponds
to the real potential difference between the most positive
and most negative points of a signal waveform.
If a sinusoidal waveform, displayed on the oscilloscope
screen, is to be converted into an effective (rms) value,
the resulting peak-to-peak value must be divided by 2x√2
= 2.83. Conversely, it should be observed that sinusoidal
voltages indicated in Vrms (Veff) have 2.83 times the potential
8
H = display height in div.,
U = signal voltage in Vpp at the vertical input,
D = deflection coefficient in V/div. at attenuator switch,
the required value can be calculated from the two given
quantities:
U=D·H
H=
U
D
D=
U
H
However, these three values are not freely selectable.
They have to be within the following limits (trigger threshold,
accuracy of reading):
Subject to change without notice
Voltage
DC + ACpeak = 400Vmax.
H between 0.5 and 8div., if possible 3.2 to 8div.,
U between 1mVpp and 160Vpp,
D between 1mV/div. and 20V/div. in 1-2-5 sequence.
Examples:
Set deflection coefficient D = 50mV/div.
0.05V/div.,
observed display height H = 4.6div.,
required voltage U = 0.05·4.6 = 0.23Vpp.
Input voltage U = 5Vpp,
set deflection coefficient D = 1V/div.,
required display height H = 5:1 = 5div.
Signal voltage U = 230Vrms·2√2 = 651Vpp
(voltage > 160Vpp, with probe 10:1: U = 65.1Vpp),
desired display height H = min. 3.2div., max. 8div.,
max. deflection coefficient D = 65.1:3.2 = 20.3V/div.,
min. deflection coefficient D = 65.1:8 = 8.1V/div.,
adjusted deflection coefficient D = 10V/div.
The input voltage must not exceed 400V, independent from the polarity. If an AC voltage which is
superimposed on a DC voltage is applied, the maximum
peak value of both voltages must not exceed + or –400V.
So for AC voltages with a mean value of zero volt the
maximum peak to peak value is 800Vpp.
If attenuator probes with higher limits are used, the
probes limits are valid only if the oscilloscope is set
to DC input coupling. If DC voltages are applied under
AC input coupling conditions the oscilloscope maximum
input voltage value remains 400V. The attenuator consists
of a resistor in the probe and the 1MΩ input resistor of the
oscilloscope, which are disabled by the AC input coupling
capacity when AC coupling is selected. This also applies
to DC voltages with superimposed AC voltages. It also
must be noted that due to the capacitive resistance of the
AC input coupling capacitor, the attenuation ratio depends
on the signal frequency. For sinewave signals with
frequencies higher than 40Hz this influence is negligible.
In the GD (ground coupling) setting, the signal path is
interrupted directly beyond the input. This causes the
attenuator to be disabled again, but now for both DC and
AC voltages.
With the above listed exceptions HAMEG 10:1 probes can
be used for DC measurements up to 600V or AC voltages
(with a mean value of zero volt) of 1200Vpp. The 100:1
probe HZ53 allows for 1200V DC or 2400Vpp for AC.
It should be noted that its ACpeak value is derated at higher
frequencies. If a normal x10 probe is used to measure high
voltages there is the risk that the compensation trimmer
bridging the attenuator series resistor will break down
causing damage to the input of the oscilloscope. However,
if for example only the residual ripple of a high voltage is
to be displayed on the oscilloscope, a normal x10 probe is
sufficient. In this case, an appropriate high voltage capacitor
(approx. 22-68nF) must be connected in series with the
input tip of the probe.
Subject to change without notice
peak
AC
DC
DC
AC
time
Total value of input voltage
The dotted line shows a voltage alternating at zero volt level. If superimposed on a DC voltage, the addition of the positive peak and the DC
voltage results in the max. voltage (DC + ACpeak).
With Y-POS. control (input coupling to GD) it is possible
to use a horizontal graticule line as reference line for
ground potential before the measurement. It can lie
below or above the horizontal central line according to
whether positive and/or negative deviations from the
ground potential are to be measured.
Time Measurements
As a rule, most signals to be displayed are periodically
repeating processes, also called periods. The number of
periods per second is the repetition frequency. Depending
on the time base setting of the TIME/DIV. switch, one or
several signal periods or only a part of a period can be
displayed. The time coefficients are stated in s/div., ms/
div. and µs/div. on the TIME/DIV.-switch. The scale is
accordingly divided into three fields.
The duration of a signal period or a part of it is
determined by multiplying the relevant time (horizontal distance in div.) by the time coefficient set on
the TIME/DIV.-switch.
The variable time control (identified with an arrow
knob cap) must be in its calibrated position CAL.
(arrow pointing horizontally to the right).
With the designations
L = displayed wave length in div. of one period,
T = time in seconds for one period,
F = recurrence frequency in Hz of the signal,
Tc = time coefficient in s/div. on timebase switch and
the relation F = 1/T, the following equations can be stated:
T = L · Tc
F=
1
L · Tc
T
Tc
1
L=
F · Tc
L=
T
L
1
Tc = L · F
Tc =
With depressed X-MAG. (x10) pushbutton the Tc
value must be divided by 10.
However, these four values are not freely selectable.
They have to be within the following limits:
L between 0.2 and 10div., if possible 4 to 10div.,
T between 0.01µs and 2s,
F between 0.5Hz and 30MHz,
Tc between 0.1µs/div. and 0.2s/div. in 1-2-5 sequence
(with X-MAG. (x10) in out position), and
Tc between 10ns/div. and 20ms/div. in 1-2-5 sequence
(with pushed X-MAG. (x10) pushbutton).
9
Examples:
Displayed wavelength L = 7div.,
set time coefficient Tc = 0.1µs/div.,
required period T = 7x0.1x10−6 = 0.7µs
required rec. freq. F = 1:(0.7x10−6) = 1.428MHz.
Signal period T = 1s,
set time coefficient Tc = 0.2s/div.,
required wavelength L = 1:0.2 = 5div..
Displayed ripple wavelength L = 1div.,
set time coefficient Tc = 10ms/div.,
required ripple freq. F = 1:(1x10x10−3) = 100Hz.
TV-line frequency F = 15625Hz,
set time coefficient Tc = 10µs/div.,
required wavelength L = 1:(15 625x10−5) = 6.4div..
Sine wavelength L = min. 4div., max. 10div.,
Frequency F = 1kHz,
max. time coefficient Tc = 1:(4x103) = 0.25ms/div.,
min. time coefficient Tc = 1:(10x103) = 0.1ms/div.,
set time coefficient Tc = 0.2ms/div.,
required wavelength L = 1:(103x0.2x10−3) = 5div.
Displayed wavelength L = 0.8div.,
set time coefficient Tc = 0.5µs/div.,
pressed X-MAG. (x10) button: Tc = 0.05µs/div.,
required rec. freq. F = 1:(0.8x0.05x10−6) = 25MHz,
required period T = 1:(25x10−6) = 40ns.
If the time is relatively short as compared with the
complete signal period, an expanded time scale should
always be applied (X-MAG. (x10) button pressed). In this
case, the ascertained time values have to be divided by
10. The time interval of interest can be shifted to the
screen center using the X-POS. control.
When investigating pulse or square waveforms, the critical
feature is the risetime of the voltage step. To ensure
that transients, ramp-offs, and bandwidth limits do not
unduly influence the measuring accuracy, the risetime is
generally measured between 10% and 90% of the vertical
pulse height. For measurement adjust the Y attenuator
switch with its variable control together with the Y-POS.
control so that the pulse height is precisely aligned with
the 0 and 100% lines of the internal graticule. The 10%
and 90% points of the signal will now coincide with the
10% and 90% graticule lines. The risetime is given by
the product of the horizontal distance in div. between
these two coincidence points and the time coefficient
setting. If X x10 magnification is used, this product must
be divided by 10. The fall time of a pulse can also be
measured by using this method.
The following figure shows correct positioning of the
oscilloscope trace for accurate risetime measurement.
10
With a time coefficient of 0.2µs/div. and pushed X-MAG
x10 button the example shown in the above figure results
in a measured total risetime of
ttot = 1.6div·0.2µs/div.:10 = 32ns
When very fast risetimes are being measured, the risetimes
of the oscilloscope amplifier and of the attenuator probe
has to be deducted from the measured time value. The
risetime of the signal can be calculated using the following
formula.
tr = √ttot2 - tosc2 - tp2
In this ttot is the total measured risetime, tosc is the risetime
of the oscilloscope amplifier (approx. 12ns), and tp the
risetime of the probe (e.g. = 2ns). If ttot is greater than
100ns, then ttot can be taken as the risetime of the pulse,
and calculation is unnecessary.
Calculation of the example in the figure above results in a
signal risetime
tr = √ 322 - 122 - 22 = 29.6ns
The measurement of the rise or fall time is not limited to
the trace dimensions shown in the above diagram. It is
only particularly simple in this way. In principle it is
possible to measure in any display position and at any
signal amplitude. It is only important that the full height of
the signal edge of interest is visible in its full length at not
too great steepness and that the horizontal distance at
10% and 90% of the amplitude is measured. If the edge
shows rounding or overshooting, the 100% should not be
related to the peak values but to the mean pulse heights.
Breaks or peaks (glitches) next to the edge are also not
taken into account. With very severe transient distortions,
the rise and fall time measurement has little meaning. For
amplifiers with approximately constant group delay
(therefore good pulse transmission performance) the
following numerical relationship between rise time tr (in
ns) and bandwidth B (in MHz) applies:
tr =
350
B
B=
350
tr
Connection of Test Signal
Caution: When connecting unknown signals to the oscilloscope input, always use automatic triggering and set the
DC-AC input coupling switch toAC. The attenuator switch
should initially be set to 20V/div.
Subject to change without notice
Sometimes the trace will disappear after an input signal
has been applied. The attenuator switch must then be
turned back to the left, until the vertical signal height is
only 3-8div. With a signal amplitude greater than 160Vpp,
an attenuator probe must be inserted before the vertical
input. If, after applying the signal, the trace is nearly
blanked, the period of the signal is probably substantially
longer than the set value on the TIME/DIV. switch. It
should be turned to the left to an adequately larger time
coefficient.
utilized (e.g. for pulses with steep edges) we strongly
advise using the modular probes HZ 51 (x10) HZ 52 (x10
HF) and HZ 54 (x1 and x10. This can save the purchase
of an oscilloscope with larger bandwidth and has the
advantage that defective components can be ordered
from HAMEG and replaced by oneself. The probes
mentioned have a HF-calibration in addition to low
frequency calibration adjustment. Thus a group delay
correction to the upper limit frequency of the oscilloscope
is possible with the aid of an 1MHz calibrator, e.g. HZ60.
The signal to be displayed can be connected directly to
the Y-input of the oscilloscope with a shielded test
cable such as HZ 32 or HZ 34, or reduced through a x10
or x100 attenuator probe. The use of test cables with
high impedance circuits is only recommended for
relatively low frequencies (up to approx. 50 kHz). For
higher frequencies, the signal source must be of low
impedance, i.e. matched to the characteristic resistance
of the cable (as a rule 50 Ohm). Especially when
transmitting square and pulse signals, a resistor equal
to the characteristic impedance of the cable must also
be connected across the cable directly at the Y-input of
the oscilloscope. When using a 50Ω cable such as the
HZ 34, a 50Ω through termination type HZ22 is available
from HAMEG. When transmitting square signals with
short rise times, transient phenomena on the edges
and top of the signal may become visible if the correct
termination is not used. A terminating resistance is
sometimes recommended with sine signals as well.
Certain amplifiers, generators or their attenuators
maintain the nominal output voltage independent of
frequency only if their connection cable is terminated
with the prescribed resistance. Here it must be noted
that the terminating resistor HZ22 will only dissipate a
maximum of 2 Watts. This power is reached with 10
Vrms or at 28.3 Vpp with sine signal.
In fact the bandwidth and rise time of the oscilloscope are
not noticably changed with these probe types and the
waveform reproduction fidelity can even be improved
because the probe can be matched to the oscilloscopes
individual pulse response.
If a x10 or x100 attenuator probe is used, no termination
is necessary. In this case, the connecting cable is matched
directly to the high impedance input of the oscilloscope.
When using attenuators probes, even high internal
impedance sources are only slightly loaded (approx. 10
MΩ II 16 pF or 100 MΩ II 9 pF with HZ 53). Therefore, if
the voltage loss due to the attenuation of the probe can be
compensated by a higher amplitude setting, the probe
should always be used. The series impedance of the
probe provides a certain amount of protection for the input
of the vertical amplifier. Because of their separate
manufacture, all attenuator probes are only partially
compensated, therefore accurate compensation must be
performed on the oscilloscope (see “Probe compensation
page M7).
Standard attenuator probes on the oscilloscope normally
reduce its bandwidth and increase the rise time. In all
cases where the oscilloscope bandwidth must be fully
Subject to change without notice
If a x10 or x100 attenuator probe is used, DC input
coupling must always be used at voltages above
400V. With AC coupling of low frequency signals, the
attenuation is no longer independent of frequency,
pulses can show pulse tilts. Direct voltages are
suppressed but load the oscilloscope input coupling
capacitor concerned. Its voltage rating is max. 400 V
(DC + peak AC). DC input coupling is therefore of quite
special importance with a x100 attenuation probe which
usually has a voltage rating of max. 1200 V (DC + peak
AC). A capacitor of corresponding capacitance and
voltage rating may be connected in series with the
attenuator probe input for blocking DC voltage (e.g. for
hum voltage measurement).
With all attenuator probes, themaximum AC input voltage
must be derated with frequency usually above 20kHz.
Therefore the derating curve of the attenuator probe type
concerned must be taken into account.
The selection of the ground point on the test object is
important when displaying small signal voltages. It should
always be as close as possible to the measuring point. If
this is not done, serious signal distortion may result from
spurious currents through the ground leads or chassis
parts. The ground leads on attenuator probes are also
particularly critical. They should be as short and thick as
possible. When the attenuator probe is connected to a
BNC-socket, a BNC-adapter, which is often supplied as
probe accessory, should be used. In this way ground and
matching problems are eliminated.
Hum or interference appearing in the measuring circuit
(especially when a small deflection coefficient is used) is
possibly caused by multiple grounding because equalizing
currents can flow in the shielding of the test cables
(voltage drop between the protective conductor
connections, caused by external equipment connected to
the mains/line, e.g. signal generators with interference
protection capacitors).
11
First Time Operation
Before applying power to the oscilloscope it is recommended that the following simple procedures are
performed:
• Check that all pushbuttons are in the out position, i.e.
released.
• Rotate the variable controls with arrows, i.e. TIME/DIV.
variable control, CH.I and CH.II attenuator variable
controls, and HOLD OFF control to their calibrated
detent.
• Set all controls with marker lines to their midrange
position (marker lines pointing vertically).
• The TRIG. selector lever switch in the X-field should be
set to the position uppermost.
• Both GD input coupling pushbutton switches for CH.I
and CH.II in the Y-field should be set to theGD position.
Switch on the oscilloscope by depressing the red POWER
pushbutton. An LED will illuminate to indicate working
order. The trace, displaying one baseline, should be visible
after a short warm-up period of approx. 10 seconds.
AdjustY-POS.I andX-POS. controls to center the baseline.
Adjust INTENS. (intensity) and FOCUS controls for
medium brightness and optimum sharpness of the trace.
The oscilloscope is now ready for use.
If only a spot appears (CAUTION! CRT phosphor can be
damaged), reduce the intensity immediately and check
that the XY pushbutton is in the released (out) position. If
the trace is not visible, check the correct positions of all
knobs and switches (particularly AT/NORM. button in out
position).
To obtain the maximum life from the cathode-ray tube, the
minimum intensity setting necessary for the measurement
in hand and the ambient light conditions should be used.
Particular care is required when a single spot is
displayed, as a very high intensity setting may cause
damage to the fluorescent screen of the CRT. Switching
the oscilloscope off and on at short intervals stresses the
cathode of the CRT and should therefore be avoided.
The instrument is so designed that even incorrect operation
will not cause serious damage. The pushbuttons control
only minor functions, and it is recommended that before
commencement of operation all pushbuttons are in the
“out” position. After this the pushbuttons can be operated
depending upon the mode of operation required.
The HM303 accepts all signals from DC (direct voltage) up
to a frequency of at least 30MHz (−3dB). For sinewave
voltages the upper frequency limit will be 50MHz (−6dB).
12
However, in this higher frequency range the vertical
display height on the screen is limited to approx. 4-5div.
The time resolution poses no problem. For example, with
50MHz and the fastest adjustable sweep rate (10ns/div.),
one cycle will be displayed every 2div. The tolerance on
indicated values amounts to ±3% in both deflection
directions. All values to be measured can therefore be
determined relatively accurately.
However, from approximately 10MHz upwards the
measuring error will increase as a result of loss of gain. At
18MHz this reduction is about 10%. Thus, approximately
11% should be added to the measured voltage at this
frequency. As the bandwidth of the amplifiers may differ
slightly (normally between 30 and 35MHz), the measured
values in the upper frequency range cannot be defined
exactly. Additionally, as already mentioned, for frequencies
above 30MHz the dynamic range of the display height
steadily decreases. The vertical amplifier is designed so
that the transmission performance is not affected by its
own overshoot.
Trace Rotation TR
In spite of Mumetal-shielding of the CRT, effects of
the earths magnetic field on the horizontal trace
position cannot be completely avoided. This is
dependent upon the orientation of the oscilloscope
on the place of work. A centred trace may not align
exactly with the horizontal center line of the graticule.
A few degrees of misalignment can be corrected by a
potentiometer accessible through an opening on the
front panel marked TR.
Probe compensation and use
To display an undistorted waveform on an oscilloscope,
the probe must be matched to the individual input
impedance of the vertical amplifier.
For this purpose a square wave signal with a very fast rise
time and minimum overshoot should be used, as the
sinusoidal contents cover a wide frequency range. The
frequency accuracy and the pulse duty factor are not of
such importance.
The built-in calibration generator provides a square wave
signal with a very fast risetime (<4ns), and switchselectable frequencies of approx. 1kHz and 1MHz from
two output sockets below the CRT screen.
This signal should not be used for frequency calibration!
Subject to change without notice
One output provides 0.2Vpp ±1% (tr <4ns) for 10:1 probes,
and the other 2Vpp ±1% for 100:1 probes. When the
attenuator switches are set to5mV/div vertical deflection
coefficient, these calibration voltages correspond to a
screen amplitude of 4div.
The output sockets have an internal diameter of 4.9mm to
accommodate the internationally accepted shielding tube
diameter of modern Modular Probes and F-series slimline
probes. Only this type of construction ensures the extremly
short ground connections which are essential for an
undistorted waveform reproduction of non-sinusoidal high
frequency signals.
Adjustment at 1kHz
The C-trimmer adjustment compensates the capacitive
loading on the oscilloscope input (approx. 20 pF for the
HM 303). By this adjustment, the capacitive division
assumes the same ratio as the ohmic voltage divider to
ensure the same division ratio for high and low frequencies,
as for DC. (For 1:1 probes or switchable probes set to 1:1,
this adjustment is neither required nor possible). A baseline
exactly parallel to the horizontal graticule lines is a major
condition for accurate probe adjustments. (See also “Trace
rotation TR”).
Connect the probes (Types HZ51, 52, 53, 54, or HZ36) to
the CH.I input. All pushbuttons should be released (in the
out position). Set input coupling to DC, the attenuator to
5 mV/div., and TIME/DIV. switch to 0.2 ms/div., and all
variable controls to CAL. position. Plug the the probe tip
into the appropriate calibrator output socket, i.e. 10:1
probes into the 0.2V socket, 100:1 probes into the 2V
socket.
1 kHz
incorrect
correct
incorrect
Only this compensative adjustment ensures optimum
utilisation of the full bandwidth, together with constant
group delay at the high frequency end, thereby reducing
characteristic transient distortion near the leading edge
(e.g. overshoot, rounding, ringing, holes or bumps) to an
absolute minimum.
Using the probes HZ51, 52 and 54, the full bandwidth of
the HM303 can be utilized without risk of unwanted
waveform distortion.
Prerequisite for this HF compensation is a square wave
generator with fast risetime (typically 4 ns), and low
output impedance (approx. 50Ω), providing 0.2V and 2V at
a frequency of approx. 1MHz. The calibrator output of the
HM303 meets these requirements when the CAL.
pushbutton is depressed.
Connect the probe to CH.I input. Depress the CAL.
pushbutton for 1MHz. All other pushbuttons should be
released (out position). Set the CH.I input coupling to DC,
attenuator switch to 5mV/div, and TIME/DIV. switch to
0.2µs/div. Set all variable controls to CAL. position.
Insert the probe tip into the output socket marked 0.2V.
A waveform will be displayed on the CRT screen, with
leading and trailing edges clearly visible. For the HFadjustment now to be performed, it will be necessary to
observe the rising edge as well as the upper left corner of
the pulse top. The connecting boxes of the HZ51 and
HZ54 contain one R-trimmer screw each, while that of the
HZ52 provides three. These R-trimmers have to be adjusted
such that the beginning of the pulse is as straight as
possible. Overshoot or excessive rounding are unacceptable. This is relatively easy on the HZ51 and HZ54, but
slightly more difficult on the HZ52. The rising edge should
be as steep as possible, with a pulse top remaining as
straight and horizontal as possible.
On the HZ52, each of the three trimmers has a clearly
defined area of influence on the waveform shape (see
Fig.), offering the added advantage of being able to
straighten out waveform abberations near the leading
edge.
HZ51, HZ54
Approximately 2 complete waveform periods are displayed
on the CRT screen. Now the compensation trimmer has to
be adjusted. Normally, this trimmer is located in the probe
head. On the 100:1 probe HZ53, however, it is located in the
connecting box at the other end of the cable. Adjust the
trimmer with the insulating screw driver provided until the
tops of the square wave signal are exactly parallel to the
horizontal graticule lines (see 1 kHz diagram). The signal
height should then be 4 div. ± 0.12div. (= 3 %). During this
adjustment, the signal edges will remain invisible.
Adjustment at 1MHz
Probes HZ51, 52 and 54 can also be HF-compensated.
They incorporate resonance de-emphasing networks (Rtrimmer in conjunction with inductances and capacitors)
which permit probe compensation in the range of the
upper frequency limit of the vertical oscilloscope amplifier.
Subject to change without notice
(LF)
(LF)
T3: alters the middle frequencies
T4: alters the leading edge
T5: alters the lower frequencies
13
After completion of the HF-adjustment, the signal amplitude
displayed on the CRT screen should have the same value
as during the 1kHz adjustment.
incorrect
incorrect
correct
Adjustment
1MHz
Probes other than those mentioned above, normally
have a larger tip diameter and may not fit into the
calibrator outputs. Whilst it is not difficult for an
experienced operator to build a suitable adapter, it
should be pointed out that most of these probes have
a slower risetime with the effect that the total bandwidth
of scope together with probe may fall far below that of
the HM303. Furthermore, the HF-adjustment feature is
nearly always missing so that waveform distortion can
not be entirely excluded.
Operating modes of the vertical amplifiers
The vertical amplifier is set to the desired operating mode
by using the 3 pushbuttons (CH I/II, DUAL and ADD) in the
Y field of the front panel. For Mono mode all 3 buttons
must be in their released positions; only channel I can then
be operated. The button CH I/II-TRIG.I/II must be depressed
in mono mode for Channel II. The internal triggering is
simultaneously switched over to Channel II with this
button.
If the DUAL button is depressed, both channels are
working. Two signals can be displayed together in this
button position (alternate mode) if the time-base setting
and the repetition frequency of the signal are suited. This
mode is not suitable for displaying very slow-running
processes. The display then flickers too much or it appears
to jump. If the ADD button is depressed in addition to
DUAL, both channels are switched over constantly at a
high frequency within a sweep period (CHOP mode). Low
frequency signals below 1kHz, or with periods longer
than 1ms are then also displayed without flicker. CHOP
mode is not recommended for signals with higher repetition
frequencies.
If only the ADD button is depressed, the signals of both
channels are algebraically added (±I ±II). Whether the
resulting display shows thesum ordifference is dependent
on the phase relationship or the polarity of the signals and
on the positions of the INVERT buttons.
In-phase input voltages:
The adjustment sequence must be followed in the order
described, i.e. first at 1kHz, then at 1MHz. The calibrator
frequencies should not be used for timebase calibration.
The pulse duty cycle deviates from 1:1 ratio.
Prerequisites for precise and easy probe adjustments, as
well as checks of deflection coefficients, are straight
horizontal pulse tops, calibrated pulse amplitude, and
zero-potential at the pulse base. Frequency and duty cycle
are relatively uncritical. For interpretation of transient
response, fast pulse risetimes and low-impedance
generator outputs are of particular importance.
Providing these essential features, as well as switchselectable output-frequencies, the calibrator of the HM303
can, under certain conditions, replace expensive
squarewave generators when testing or compensating
wideband-attenuators or -amplifiers. In such a case, the
input of an appropriate circuit will be connected to one of
the CAL.-outputs via a suitable probe.
The voltage provided at a high-impedance input (1MΩII1550pF) will correspond to the division ratio of the probe
used (10:1 = 20mVpp, 100:1 = also 20mVpp from 2V
output). Suitable probes are HZ51, 52, 53, and 54.
14
Both INVERT CH.I and INVERT CH.II buttons
released or depressed = sum.
Only one INVERT button depressed = difference.
Antiphase input voltages:
Both INVERT buttons released or depressed
= difference.
INVERT CH.Ior INVERT CH.II button depressed = sum.
In theADD mode the vertical display position is dependent
upon the Y-POS. setting of both channels. The same
attenuator switch position is normally used for both
channels with algebraic addition.
Please note that the Y-POS. settings are added too but are
not affected by the INVERT pushbuttons.
Differential measurement techniques allow direct
measurement of the voltage drop across floating
components (both ends above ground). Two identical
probes should be used for both vertical inputs. In order to
avoid ground loops, use a separate ground connection and
do not use the probe ground leads or cable shields.
Subject to change without notice
X-Y Operation
The following must be noted here:
For X-Y operation, the pushbutton in the X field marked
XY must be depressed. The X signal is then derived from
the INPUT CH II (X). The calibration of the X signal
during X-Y operation is determined by the setting of
the Channel II input attenuator and variable control.
− Because of the periodic nature of the trigonometric
functions, the calculation should be limited to angles
≤90°. However here is the advantage of the method.
This means that the sensitivity ranges and input
impedances are identical for both the X and Y axes.
However, the Y-POS.II control is disconnected in this
mode. Its function is taken over by the X-POS. control. It
is important to note that the X-MAG. (x10) facility,
normally used for expanding the sweep, should not be
operated in the X-Y mode. It should also be noted that the
bandwidth of the X amplifier is≥3MHz (−3dB), and therefore
an increase in phase difference between both axes is
noticeable from 50kHz upwards.
The inversion of the X-input signal using theINVERT CH.II
button is not possible.
Lissajous figures can be displayed in the X-Y mode for
certain measuring tasks:
− Comparing two signals of different frequency or bringing
one frequency up to the frequency of the other signal.
This also applies for whole number multiples or fractions
of the one signal frequency.
− Do not use a too high test frequency. The phase shift
of the two oscilloscope amplifiers of the HM 303 in the
X-Y mode can exceed an angle of 3° above 120 kHz.
− It cannot be seen as a matter of course from the screen
display if the test voltage leads or lags the reference
voltage. A CR network before the test voltage input of
the oscilloscope can help here. The 1 MΩ input resistance can equally serve as R here, so that only a
suitable capacitor C needs to be connected in series. If
the aperture width of the ellipse is increased (compared
with C short-circuited), then the test voltage leads the
reference voltage and vice versa. This applies only in
the region up to 90° phase shift. Therefore C should be
sufficiently large and produce only a relatively small just
observable phase shift.
Should both input voltages be missing or fail in the
X-Y mode, a very bright light dot is displayed on the
screen. This dot can burn into the phosphor at a too
high brightness setting (INTENS. knob) which causes
either a lasting loss of brightness, or in the extreme
case, complete destruction of the phosphor at this
point.
− Phase comparison between two signals of the same
frequency.
Phase comparison with Lissajous figures
The following diagrams show two sine signals of the
same frequency and amplitude with different phase angles.
Calculation of the phase angle or the phase shift between
the X and Y input voltages (after measuring the distances
a and b on the screen) is quite simple with the following
formula, and a pocket calculator with trigonometric
functions. Apart from the reading accuracy, the signal
height has no influence on the result.
sin ϕ = a
b
cos ϕ =
√
1−
−
( ba )
2
ϕ = arc sin a
b
Subject to change without notice
Phase difference measurement
in DUAL mode
A larger phase difference between two input signals of
the same frequency and shape can be measured very
simply on the screen in Dual mode (DUAL button
depressed). The time base should be triggered by the
reference signal (phase position 0). The other signal can
then have a leading or lagging phase angle. Alternate
mode should be selected for frequencies ≥1 kHz; the
Chop mode is more suitable for frequencies <1 kHz (less
flickering).
For greatest accuracy adjust not much more than one
period and approximately the same height of both signals
on the screen. The variable controls for amplitude and
time base and the LEVEL knob can also be used for this
adjustment without influence on the result. Both base
lines are set onto the horizontal graticule center line with
the Y-POS. knobs before the measurement. With
sinusoidal signals, observe the zero (crossover point)
transitions; the sine peaks are less accurate. If a sine
signal is noticeably distorted by even harmonics, or if a d.c.
voltage is present, AC coupling is recommended for both
channels. If it is a question of pulses of the same shape,
read off at steep edges.
15
Phase difference measurement in DUAL mode
t = horizontal spacing of the zero transitions in div.
T = horizontal spacing for one period in div.
button depressed) using a suitable LEVEL setting and
possibly also using the time variable adjustment.
Oscilloscope setting for a signal according to figure 2:
Depress no buttons. Y: CH. I; 20mV/div.; AC.
TIME/DIV.: 0.2ms/div.
Triggering: NORMAL; with LEVEL-setting; internal (or
external) triggering.
m • UT
UT
a
b
In the example illustrated, t = 3div. and T = 10div. The
phase difference in degrees is calculated from
ϕ° = t · 360° = 3 · 360° = 108°
10
T
arc ϕ° = t · 2π = 3 · 2π = 1,885 rad
10
T
Relatively small phase angles at not too high frequencies
can be measured more accurately in the X-Y mode with
Lissajous figures.
Measurement of an amplitude modulation
The momentary amplitude u at time t of a HF-carrier
voltage, which is amplitude modulated without distortion
by a sinusoidal AF voltage, is in accordance with the
equation
u = UT · sinΩt + 0,5m · UT · cos(Ω−ω)t − 0,5m · UT · cos(Ω+ω)t
where
UT
Ω
ω
m
= unmodulated carrier amplitude
= 2πF = angular carrier frequency
= 2πf = modulation angular frequency
= modulation factor (i.a. ≤ 1 100%).
The lower side frequencyF−f and the upper side frequency
F+f arise because of the modulation apart from the carrier
UT
frequency F.
0 . 5 m • UT
Figure 1
F–f
0 . 5 m • UT
F+f
Amplitude and frequency spectrum for AM display (m = 50%)
The display of the amplitude-modulated HF oscillation can
be evaluated with the oscilloscope provided the frequency
spectrum is inside the oscilloscope bandwidth. The time
base is set so that several wave of the modulation
frequency are visible. Strictly speaking, triggering should
be external with modulation frequency (from the AF
generator or a demodulator). However, internal triggering
is frequently possible with normal triggering (AT/NORM.
16
Figure 2
Amplitude modulated oscillation: F = 1 MHz; f = 1 kHz;
m = 50 %; UT = 28.3 mVrms.
If the two values a and b are read from the screen, the
modulation factor is calculated from
m=a−b
a+b
or
m = a − b · 100 [%]
a+b
where a = UT (1+m) and b = UT (1−m)..
The variable controls for amplitude and time can be set
arbitrarily in the modulation factor measurement. Their
position does not influence the result.
Triggering and time base
Time related amplitude changes on a measuring signal
(AC voltage) are displayable in Yt-mode. In this mode the
signal voltage deflects the beam in vertical direction while
the timebase generator moves the beam from the left to
the right of the screen (time deflection).
Normally there are periodically repeating waveforms to be
displayed. Therefore the time base must repeat the time
deflection periodically too. To produce a stationary display,
the time base must only be triggered if the signal height
and slope condition coincide with the former time base
start conditions. A DC voltage signal can not be triggered
as it is a constant signal with no slope.
Triggering can be performed by the measuring signal itself
(internal triggering) or by an external supplied but
synchronous voltage (external triggering).
The trigger voltage should have a certain minimum
amplitude. This value is called the trigger threshold. It is
measured with a sine signal. When the trigger voltage is
taken internally from the test signal, the trigger threshold
can be stated as vertical display height in div., through
which the time base generator starts, the display is stable,
and the trigger LED lights.
Subject to change without notice
The internal trigger threshold of the HM303 is given as
≤.5div. When the trigger voltage is externally supplied, it
can be measured in Vpp at theTRIG. INP. socket. Normally,
the trigger threshold may be exceeded up to a maximum
factor of 20.
The HM303 has two trigger modes, which are characterized
in the following.
Automatic Triggering
If the AT/NORM. pushbutton in the X field is in the out
position AT, the sweep generator is running without test
signal or external trigger voltage. A base line is always
displayed even without a signal applied. This trigger mode
is therefore called Automatic Triggering. Operation of
the scope needs, having a constantly visible trace, only a
correct amplitude and time base setting. A LEVEL
adjustment is neither necessary nor possible with automatic triggering. This simple AT mode is recommended
for all uncomplicated measuring tasks such as DC voltage
measuring. However, automatic triggering is also the
appropriate operation mode for the "entry" into difficult
measuring problems, e.g. when the test signal is unknown
relating to amplitude, frequency or shape. Presetting of all
parameters is now possible with automatic triggering; the
change to normal triggering can follow thereafter.
The automatic triggering works above20Hz.. The changeover to the break down of the automatic triggering at
frequencies below 20Hz is abrupt. However, it can not be
recognized by the TRIG. LED; this is still blinking. Break
down of triggering is best recognizable at the left screen
edge (the start of the trace in differing display height).
If the pulse duty factor of a square-wave signal changes
so much that one part of the square-wave reduces to a
needle pulse, switching over to normal triggering and
using the LEVEL control can be necessary. With automatic
triggering, the trigger point lies approx. in the zero voltage
crossing. The time interval, required for the time base
start, can be too short at a steep zero crossing of the
needle pulse. Then normal triggering should be used.
Automatic triggering is practicable not only with internal
but also with external trigger voltage.
Normal Triggering
With normal triggering (AT/NORM. button depressed)
and LEVEL adjustment, the sweep can be started by AC
signals within the frequency range selected by the TRIG.
coupling switch. In the absence of an adequate trigger
signal or when the trigger controls (particularly the
LEVEL control) are misadjusted, no trace is visible,
i.e. the screen blanked completely.
When using the internal normal triggering mode, it is
possible to trigger at any amplitude point of a signal edge,
even with very complex signal shapes, by adjusting the
LEVEL control. Its adjusting range is directly dependent
on the display height, which should be at least 0.5div. If
it is smaller than 1div., the LEVEL adjustment needs to be
operated with a sensitive touch. In the external normal
Subject to change without notice
triggering mode, the same applies to approx. 0.3V external
trigger voltage amplitude.
Other measures for triggering of very complex signals are
the use of the time base variable control and HOLDOFF
time control, hereinafter mentioned.
Slope
The time base generator can be started by a rising or falling
edge of the test signal. This is valid with automatic and
with normal triggering. The selected slope is set with the
SLOPE (+/–) pushbutton. The plus sign (button released)
means an edge, which is coming from a negative potential
and rising to a positive potential. That has nothing to do
with zero or ground potential and absolute voltage values.
The positive slope may also lie in a negative part of a
signal. A falling edge (minus sign) triggers, when theSLOPE
(+/–) pushbutton is depressed.
However the trigger point may be varied within certain
limits on the chosen edge using the LEVEL control. The
slope direction is always related to the input signal and the
non inverted display.
.
Trigger coupling
The coupling mode and accordingly the frequency range
of the trigger signal can be changed using the TRIG.
selector switch.
AC: Trigger range <20Hz to 100MHz.
This is the most frequently used trigger mode. The
trigger threshold is increasing below 20Hz and above
100MHz.
DC: Trigger range DC to 100MHz.
DC triggering is recommended, if the signal is to be
triggered with quite slow processes or if pulse signals
with constantly changing pulse duty factors have to
be displayed.
With DC- or LF-trigger coupling, always work
with normal triggering and LEVEL adjustment.
LF: Trigger range DC to 1.5kHz (low-pass filter).
The LF position is often more suited for low-frequency
signals than the DC position, because the (white) noise
in the trigger voltage is strongly suppressed. So jitter or
double-triggering of complex signals is avoidable or at
least reduced, in particular with very low input voltages.
The trigger threshold increases above 1.5kHz.
TV: The built-in active TV-Sync-Separator enables the
separation of sync pulses from the video signal. Even
distorted video signals are triggered and displayed in
a stable manner.
Video signals are triggered in the automatic mode. The
internal triggering is virtually independent of the display
height, but the sync pulse must exceed 0.5div. height. For
TV sync pulse separation the TRIG. switch must be set to
TV. The TIME/DIV.-switch selects between field (.2s/
div. - .2ms/div.) and line (.1ms/div. - .1µs/div.).
17
The slope of the leading edge of the synchronization pulse
is critical for theSLOPE pushbutton setting. If the displayed
sync pulses are above the picture (field) contents, then
the SLOPE pushbutton (±) must be in + position (out). In
the case of sync pulses below the field/line, the leading
edge is negative and the SLOPE pushbutton must therefore
be depressed (to “–”). Since the INVERT function may
cause a misleading display, it must not be activated until
after correct triggering is achieved.
On the 2ms/div setting field TV triggering is selected and
1 field is visible if a 50 fields/s signal is applied. If the hold
off control is in fully ccw position, it triggers without line
interlacing affects caused by the consecutive field. More
details in the video signal become visible if the X-MAG.
(x10) pushbutton is depressed (in). The X-POS. control
allows to display any part of the expanded signal. The
influence of the integrating network which forms a trigger
pulse from the vertical sync pulses may become visible
under certain conditions.
Disconnecting the trigger circuit (e.g. by rapidly pressing
and releasing the EXT. button) can result in triggering the
consecutive (odd or even) field.
On the 10µs/div setting line TV triggering is selected and
approx. 1½ lines are visible. Those lines originate randomly
from the odd and even fields.
The sync-separator-circuit also operates with external
triggering. It is important that the voltage range (0.3Vpp to
3Vpp) for external triggering should be noted. Again the
correct slope setting is critical, because the external
trigger signal may not have the same polarity or pulse
edge as the test signal. This can be checked, if the
external trigger voltage itself is displayed first (with internal
triggering).
In most cases, the composite video signal has a high DC
content. With constant video information (e.g. test pattern or
color bar generator), the DC content can be suppressed
easily byAC input coupling of the oscilloscope amplifier.With
a changing picture content (e.g. normal program), DC input
coupling is recommended, because the display varies its
vertical position on screen with AC input coupling at each
change of the picture content. The DC content can be
compensated using the Y-POS. control so that the signal
display lies in the graticule area. Then the composite video
signal should not exceed a vertical height of 6div.
Line triggering (~)
A voltage originating from mains/line (50 to 60Hz) is used
for triggering purposes if the TRIG. switch is set to ~. This
trigger mode is independent of amplitude and frequency of
the Y signal and is recommended for all mains/line
synchronous signals. This also applies within certain limits
to whole number multiples or fractions of the line frequency.
Line triggering can also be useful to display signals below the
trigger threshold (less than 0.5div). It is therefore particularly
suitable for measuring small ripple voltages of mains/line
rectifiers or stray magnetic field in a circuit. In this trigger
mode the SLOPE pushbutton selects the positive or negati18
ve portion of the line sinewave. TheLEVEL control is used for
trigger point adjustment in case of normal triggering (AT/
NORM. depressed).
Magnetic leakage (e.g. from a power transformer) can be
investigated for direction and amplitude using a search or
pick-up coil. The coil should be wound on a small former
with a maximum of turns of a thin lacquered wire and
connected to a BNC connector (for scope input) via a
shielded cable. Between cable and BNC center conductor
a resistor of at least 100Ω should be series-connected (RF
decoupling). Often it is advisable to shield statically the
surface of the coil. However, no shorted turns are
permissible. Maximum, minimum, and direction to the
magnetic source are detectable at the measuring point by
turning and shifting the coil.
Alternate triggering
With alternate triggering (ALT. button depressed) it is
possible to trigger two signals which are different in frequency
(asynchronous). In this case the oscilloscope must be operated
in alternate DUAL mode with signals of sufficient height at
each input. To avoid trigger problems due to different DC
voltage components,AC input coupling for both channels is
recommended.
The internal trigger source is switched in the same way as
the channel switching after each time base sweep.
Phase difference measurement is not possible in this
trigger mode.
External triggering
The internal triggering is disconnected by depressing the
TRIG. EXT. button. The timebase can be triggered
externally via the TRIG. INP. socket using a 0.3Vpp to 3Vpp
voltage, which is in syncronism with the test signal. This
trigger voltage may have completely different form from
the test signal voltage. Triggering is even possible in
certain limits with whole number multiples or fractions of
the test frequency, but only with synchronous signals.
The input impedance of the TRIG. INP. socket is approx.
100kΩ II 10pF. The maximum input voltage of the input
circuit is 100V (DC+peak AC).
It must be noted that a different phase angle between the
measuring and the triggering signal may cause a display
not coinciding with the SLOPE pushbutton setting.
The trigger coupling selection can also be used in external
triggering mode. Unlike internal triggering, the lowest
frequency for external triggering is 20Hz in all trigger
coupling conditions.
Trigger indicator
An LED on condition (above the TRIG. switch) indicates
that the trigger signal has a sufficient amplitude and the
LEVEL control setting is correct. This is valid with automatic
and with normal triggering. The indication of trigger action
facilitates a sensitive LEVEL adjustment, particularly at
very low signal frequencies. The indication pulses are of
only 100ms duration.
Subject to change without notice
Thus for fast signals the LED appears to glow continuously,
for low repetition rate signals, the LED flashes at the
repetition rate or at a display of several signal periods not
only at the start of the sweep at the left screen edge, but
also at each signal period.
In automatic triggering mode the sweep generator starts
repeatedly without test signal or external trigger voltage. If
the trigger signal frequency is <20Hz the sweep generator
starts without awaiting the trigger pulse. This causes an
untriggered display and a flashing trigger LED (TR).
Holdoff-time adjustment
If it is found that a trigger point cannot be located on
extremely complex signals even after repeated and careful
adjustment of the LEVEL control, a stable display may be
obtained using the HOLD OFF control (in the X-field). This
facility varies the holdoff time between two sweep periods
approx. up to the ratio 10:1. Pulses or other signal waveforms appearing during this off period cannot trigger the
timebase. Particularly with burst signals or aperiodic pulse
trains of the same amplitude, the start of the sweep can
be delayed until the optimum or required moment.
A very noisy signal or a signal with a higher interfering
frequency is at times displayed double. It is possible
that LEVEL adjustment only controls the mutual
phase shift, but not the double display. The stable
single display of the signal, required for evaluation, is
easily obtainable by expanding the hold off time. To
this end the HOLD OFF knob is slowly turned to the
right, until one signal is displayed.
A double display is possible with certain pulse signals,
where the pulses alternately show a small difference of
the peak amplitudes. Only a very exactLEVEL adjustment
makes a single display possible. The use of theHOLD OFF
knob simplifies the right adjustment.
After specific use the HOLD OFF control should be reset
into its calibration detent (fully ccw), otherwise the
brightness of the display is reduced drastically. The function
is shown in the following figures.
Function of var. HOLD OFF control
heavy parts are displayed
period
signal
sweep
Fig. 1
adjusting
HOLDOFF
time
Fig. 2
Fig. 1 shows a case where theHOLD OFF knob is in the minimum position
and various different waveforms are overlapped on the screen, making
the signal observation unsuccessful.
Fig. 2 shows a case where only the desired parts of the signal are
stably displayed.
Subject to change without notice
Y Overscanning Indication
This indicator shows any vertical overscan of the usable
(10 x 8) screen area, if any part of the signal or baseline are
outside the graticule. The indication is achieved by 2 lightemitting diodes, marked OVERSCAN, which are located
between the attenuators. Should one LED illuminate
without an input signal, this means that the respective
vertical positioning control has been improperly adjusted.
Because each LED correlates with one of both possible
directions, it can be seen in which direction the trace has
left the screen. With dual channel operation, misadjustment
of both Y-POS. controls can occur. If both traces lie in the
same direction, one LED illuminates likewise. If one trace
is positioned above and the other below the graticule, both
LEDs are illuminated. The indication of the Y position after
crossing the graticule area occurs in each operating
mode, also when, due to missing time deflection, no
baseline is displayed, or when the oscilloscope is in the XY mode.
As previously written in the paragraph “First Time Operation”, the AT/NORM. pushbutton should be switched in
AT position, as a baseline is then permanently displayed,
also without any input signal. The trace disappears at
times after applying an input signal. The LED indication
shows, in which direction the trace has left the screen,
above or below the graticule. Illumination of both LEDs at
the same time after applying a signal means that the
vertical deflection has overscanned the graticule edges in
both vertical directions. With DC input coupling and an
applied signal with a relatively high DC offset, smaller
sizes also of displayed signals can overscan the raster
edges, because the DC voltage causes a vertical position
shift of the display height, which seemed correctly adjusted.
In this case, a smaller display height must be accepted, or
AC input coupling has to be selected.
Component Tester
General
The HM303 has a built-in electronic Component Tester
(COMP. TESTER), which is used for instant display of a
test pattern to indicate whether or not components are
faulty. The COMP. TESTER can be used for quick checks
of semiconductors (e.g. diodes and transistors), resistors,
capacitors, and inductors. Certain tests can also be made
to integrated circuits. All these components can be tested
in and out of circuit.
The test principle is fascinatingly simple. A built-in generator
delivers a sine voltage, which is applied across the
component under test and a built-in fixed resistor. The
sine voltage across the test object is used for the horizontal deflection, and the voltage drop across the resistor (i.e.
current through test object) is used for vertical deflection
of the oscilloscope. The test pattern shows a currentvoltage characteristic of the test object.
Since this circuit operates with a frequency of 50Hz
(±10%) and a voltage of 6V max. (open circuit), the
19
indicating range of the component tester is limited. The
impedance of the component under test is limited to a
range from 20Ω to 4.7kΩ. Below and above these values,
the test pattern shows only short-circuit or open-circuit.
For the interpretation of the displayed test pattern, these
limits should always be borne in mind. However, most
electronic components can normally be tested without
any restriction.
Using the Component Tester
The component tester is switched on by depressing the
COMP. TESTER pushbutton (on) beneath the screen.
This makes the vertical preamplifier and the timebase
generator inoperative. A shortened horizontal trace will be
observed. It is not necessary to disconnect scope input
cables unless in-circuit measurements are to be carried
out. In the COMP. TESTER mode, the only controls which
can be operated are INTENS., FOCUS, and X-POS.. All
other controls and settings have no influence on the test
operation.
For the component connection, two simple test leads
with 4mm Ø banana plugs, and with test prod, alligator clip
or sprung hook, are required. The test leads are connected
to the insulated socket and the adjacent ground socket
beneath the screen. The component can be connected to
the test leads either way round.
After use, to return the oscilloscope to normal operation,
release the COMP. TESTER pushbutton (off).
Test Procedure
Caution! Do not test any component in live circuitry
− remove all grounds, power and signals connected
to the component under test. Set up Component
Tester as stated above. Connect test leads across
component to be tested. Observe oscilloscope display.
Only discharged capacitors should be tested!
Test Pattern Displays
Page M17 shows typical test patterns displayed by the
various components under test.
• Open circuit is indicated by a straight horizontal
line.
• Short circuit is shown by a straight vertical line.
Testing Resistors
If the test object has a linear ohmic resistance, both deflecting
voltages are in the same phase. The test pattern expected
from a resistor is therefore a sloping straight line. The angle
of slope is determined by the resistance of the resistor under
test. With high values of resistance, the slope will tend
towards the horizontal axis, and with low values, the slope
20
will move towards the vertical axis.
Values of resistance from 20 Ω to 4.7k Ω can be approximately evaluated. The determination of actual values will
come with experience, or by direct comparison with a
component of a known value.
Testing Capacitors and Inductors
Capacitors and inductors cause a phase difference between
current and voltage, and therefore between the X and Y
deflection, giving an ellipse-shaped display. The position
and opening width of the ellipse will vary according to the
impedance value (at 50Hz) of the component under test.
A horizontal ellipse indicates a high impedance or a
relatively small capacitance or a relatively high
inductance.
A vertical ellipse indicates a small impedance or a
relatively large capacitance or a relatively small
inductance.
A sloping ellipse means that the component has a
considerable ohmic resistance in addition to its
reactance.
The values of capacitance of normal or electrolytic
capacitors from 0.1µF to 1000µF can be displayed and
approximate values obtained. More precise measurement
can be obtained in a smaller range by comparing the
capacitor under test with a capacitor of known value.
Inductive components (coils, transformers) can also be
tested. The determination of the value of inductance
needs some experience, because inductors have usually
a higher ohmic series resistance. However, the impedance
value (at 50Hz) of an inductor in the range from 20Ω to
4.7kΩ can easily be obtained or compared.
Testing Semiconductors
Most semiconductor devices, such as diodes, Z-diodes,
transistors, FETs can be tested. The test pattern displays
vary according to the component type as shown in the
figures below.
The main characteristic displayed during semiconductor
testing is the voltage dependent knee caused by the
junction changing from the conducting state to the non
conducting state. It should be noted that both the forward
and the reverse characteristic are displayedsimultaneously.
This is a two-terminal test, therefore testing of transistor
amplification is not possible, but testing of a single junction
is easily and quickly possible. Since the test voltage
applied is only very low, all sections of most semiconductors can be tested without damage. However,
checking the breakdown or reverse voltage of high voltage
semiconductors is not possible. More important is testing
components for open or short-circuit, which from
Subject to change without notice
experience is most frequently needed.
Testing Diodes
Diodes normally show at least their knee in the forward
characteristic. This is not valid for some high voltage diode
types, because they contain a series connection of several
diodes. Possibly only a small portion of the knee is visible.
Z-diodes always show their forward knee and, up to
approx. 7V, their Z-breakdown, forms a second knee in the
opposite direction. A Z-breakdown voltage of more than
6.8V can not be displayed.
These transistor test patterns are valid in most cases,
but there are exceptions to the rule (e.g. Darlington,
FETs). With the COMP. TESTER, the distinction
between a P-N-P to an N-P-N transistor is discenible. In
case of doubt, comparison with a known type is helpful.
It should be noted that the same socket connection
(COMP. TESTER or ground) for the same terminal is
then absolutely necessary. A connection inversion
effects a rotation of the test pattern by 180 degrees
round about the center point of the scope graticule.
In-Circuit Tests
Type:
Normal Diode
Terminals:
Cathode-Anode
Connections:
(CT-GD)
High Voltage Diode
Cathode-Anode
(CT-GD)
Z-Diode 6.8V
Cathode-Anode
(CT-GD)
The polarity of an unknown diode can be identified by
comparison with a known diode.
Testing Transistors
Three different tests can be made to transistors: baseemitter, base-collector and emitter-collector. The resulting
test patterns are shown below.
The basic equivalent circuit of a transistor is a Z-diode
between base and emitter and a normal diode with
reverse polarity between base and collector in series
connection. There are three different test patterns:
For a transistor the figures b-e and b-c are important. The
figure e-c can vary; but a vertcal line only shows short
circuit condition.
N-P-N Transistor
Terminals:
Connections:
b-e
(CT-GD)
b-c
(CT-GD)
e-c
(CT-GD)
P-N-P Transistor
Caution! During in-circuit tests make sure the circuit
is dead. No power from mains/line or battery and no
signal inputs are permitted. Remove all ground
connections including Safety Earth (pull out power
plug from outlet). Remove all measuring cables
including probes between oscilloscope and circuit
under test. Otherwise both COMP. TESTER leads are
not isolated against the circuit under test.
In-circuit tests are possible in many cases. However, they
are not well defined. This is caused by a shunt connection
of real or complex impedances − especially if they are of
relatively low impedance at 50Hz − to the component
under test, often results differ greatly when compared
with single components. In case of doubt, one component
terminal may be unsoldered. This terminal should then be
connected to the insulated COMP. TESTER socket
avoiding hum distortion of the test pattern.
Another way is a test pattern comparison to an identical
circuit which is known to be operational (likewise without
power and any external connections). Using the test
prods, identical test points in each circuit can be checked,
and a defect can be determined quickly and easily. Possibly
the device itself under test contains a reference circuit
(e.g. a second stereo channel, push-pull amplifier,
symmetrical bridge circuit), which is not defective.
The test patterns on page 22 show some typical displays
for in-circuit tests.
Terminals:
Connections:
b-e
(CT-GD)
Subject to change without notice
b-c
(CT-GD)
e-c
(CT-GD)
21
Test patterns
Single Components
Single Transistors
Short circuit
Ω
Resistor 510Ω
Junction B-C
Junction B-E
Mains transformer prim.
Capacitor 33µF
Junction E-C
FET
Single Diodes
In-circuit Semiconductors
Z-diode below 7V
Z-diode beyond 7V
Ω
Diode paralleled by 680Ω
2 Diodes antiparallel
Silicon diode
Germanium diode
Ω
Diode in series with 51Ω
Ω
B-E paralleled by 680Ω
Rectifier
Thyristor, G + A together
Ω
B-E with 1µF+680Ω
Si.-Diode with 10µF
22
Subject to change without notice
Test Instructions
General
These Test Instructions are intended as an aid for checking
the most important characteristics of the HM303 at
regular intervals without the need for expensive test
equipment. Resulting corrections and readjustments inside
the instrument, indicated by the following tests, are
described in the Service Instructions or on the Adjusting
Plan. They should only be undertaken by qualified
personnel.
As with the First Time Operation instructions, care should
be taken that all knobs with arrows are set to their
calibrated positions. None of the pushbuttons should be
depressed. TRIG. selector switch toAC. It is recommended
to switch on the instrument for about 20 minutes prior to
the commencement of any check.
Cathode-Ray Tube: Brightness and Focus,
Linearity, Raster Distortions
Normally, the CRT of the HM303 has very good brightness.
Any reduction of this brightness can only be judged
visually. However, decreased brightness may be the
result of wrong setting or reduced high voltage. The latter
is easily recognized by the greatly increased sensitivity of
the vertical amplifier. Right setting means, that the HOLD
OFF control should be turned to the left stop; the X-MAG.
(x10) button should be released; a medium time coefficient
should be selected; line triggering (~ position) should be
used only with a suitable TIME/DIV. switch setting (e.g.
2ms/div.). The control range for maximum and minimum
brightness (intensity) must be such that the beam just
disappears before reaching the left hand stop of the
INTENS. control (particularly when the XY button is
depressed), while with the control at the right hand stop
the focus and the line width are just acceptable.
With maximum intensity the timebase fly-back must
on no account be visible. Visible trace fault without
input signal: bright dot on the left side or decreasing
brightness from left to right or shortening of the baseline.
(Cause: Incorrect Unblanking Pulse.) It should be noted
that with wide variations in brightness, refocusing is
always necessary. Moreover, with maximum brightness,
no “pumping” of the display must occur. If pumping does
occur, it is normally due to a fault in the regulation circuitry
for the high voltage supply. The presetting pots for the
high voltage circuit, minimum and maximum intensity, are
only accessible inside the instrument (see Adjusting Plan
and Service Instructions).
A certain out-of-focus condition in the edge zone of the
screen must be accepted. It is limited by standards of the
CRT manufacturer. The same is valid for tolerances of the
orthogonality, the undeflected spot position, the nonlinearity and the raster distortion in the marginal zone of
Subject to change without notice
the screen in accordance with international standards
(see CRT data book). These limit values are strictly
supervised by HAMEG. The selection of a cathode-ray
tube without any tolerances is practically impossible.
Astigmatism Check
Check whether the horizontal and vertical sharpness of the
display are equal. This is best seen by displaying a squarewave signal with the repetition rate of approximately 1MHz.
Focus the horizontal tops of the square-wave signal at
normal intensity, then check the sharpness of the vertical
edges. If it is possible to improve this vertical sharpness by
turning the FOCUS control, then an adjustment of the
astigmatism control is necessary. A potentiometer of 47kΩ
is provided inside the instrument for the correction of
astigmatism (see Service Instructions). A certain loss of
marginal sharpness of the CRT is unavoidable; this is due to
the manufacturing process of the CRT.
Symmetry and Drift of the Vertical Amplifier
Both of these characteristics are substantially determined
by the input stages of the amplifiers.
The symmetry of both channels and the vertical final
amplifier can be checked by inverting Channel I and II
(depress the corresponding INVERT pushbutton). The
vertical position of the trace should not change by more
than 0.5div. However, a change of 1div. is just permissible.
Larger deviations indicate that changes have occurred in
the amplifier.
A further check of the vertical amplifier symmetry is
possible by checking the control range of the Y-POS.
controls. A sine-wave signal of 10-100kHz is applied to the
amplifier input. When the Y-POS. control is then turned
fully in both directions from stop to stop with a display
height of approximately8div., the upper and lower positions
of the trace that are visible should be approximately of the
same height. Differences of up to 1div. are permissible
(input coupling should be set to AC).
Checking the drift is relatively simple. 20 minutes after
switching on the instrument, set the baseline exactly
on the horizontal center line of the graticule. The beam
position must not change by more than 0.5div. during the
following hour.
Calibration of the Vertical Amplifier
Two square-wave voltages of 0.2Vpp and 2Vpp ±1% are
present at the output sockets of the calibrator (CAL.) If a
direct connection is made between the 0.2V output and the
23
input of the vertical amplifier (e.g. using a x1 probe), the
displayed signal in the 50mV/div. position (variable control
to CAL.) should be4div. high (DC input coupling). Maximum
deviations of 0.12div. (3%) are permissible. If ax10 probe is
connected between the 2V output and Y input, the same
display height should result. With higher tolerances it should
first be investigated whether the cause lies, within the
amplifier or in the amplitude of the square-wave signal. On
occasions it is possible that the probe is faulty or incorrectly
compensated. If necessary the measuring amplifier can be
calibrated with an accurately known DC voltage (DC input
coupling). The trace position should then vary in accordance
with the deflection coefficient set.
With variable control at the attenuator switch fully conterclockwise, the input sensitivity is decreased at least by
the factor 2.5 in each position. In the 50mV/div. position,
the displayed calibrator signal height should vary from
4div. to at least 1.6div.
Transmission Performance of the
Vertical Amplifier
The transient response and the delay distortion correction
can only be checked with the aid of a square-wave
generator with a fast risetime (max. 5ns). The signal
coaxial cable (e.g. HZ34) must be terminated at the
vertical input of the oscilloscope with a resistor equal to
the characteristic impedance of the cable (e.g. with
HZ22). Checks should be made at 100Hz, 1kHz, 10kHz,
100kHz and 1MHz, the deflection coefficient should be
set at 5mV/div. with DC input coupling (Y variable control
in CAL. position). In so doing, the square pulses must have
a flat top without ramp-off, spikes and glitches; no
overshoot is permitted, especially at 1MHz and a display
height of 4-5div.. At the same time, the leading top corner
of the pulse must not be rounded. In general, no great
changes occur after the instrument has left the factory,
and it is left to the operators discretion whether this test
is undertaken or not. A suited generator for this test is
HZ60 from HAMEG.
Of course, the quality of the transmission performance is
not only dependent on the vertical amplifier. The input
attenuators, located in the front of the amplifier, are
frequency-compensated in each position. Even small
capacitive changes can reduce the transmission
performance. Faults of this kind are as a rule most easily
detected with a square-wave signal with a low repetition
rate (e.g. 1kHz). If a suitable generator with max. output
of 40Vpp is available, it is advisable to check at regular
intervals the deflection coefficients on all positions of the
input attenuators and readjust them as necessary. A
compensated 2:1 series attenuator (e.g. HZ23) is also
necessary, and this must be matched to the input
impedance of the oscilloscope. This attenuator can be
24
T2
made up locally. It is important that this attenuator is
shielded. For local manufacture, the electrical components required are a 1MΩ ±1% resistor and, in parallel
with it, a trimmer 3-15pF in parallel with approx. 12pF.
One side of this parallel circuit is connected directly to
the input connector of CH.I or CH.II and the other side
is connected to the generator, if possible via a lowcapacitance coaxial cable. The series attenuator must
be matched to the input impedance of the oscilloscope
in the 5mV/div. position (variable control to CAL., DC
input coupling; square tops exactly horizontal; no rampoff is permitted). This is achieved by adjusting the
trimmer located in the 2:1 attenuator. The shape of
the square-wave should then be the same in each
input attenuator position.
Operating Modes: CH.I/II, DUAL, ADD,
CHOP., INVERT and X-Y Operation
On depressing the DUAL pushbutton, two traces must
appear immediately. On actuation of the Y-POS. controls,
the trace positions should have no effect on each other.
Nevertheless, this cannot be entirely avoided, even in fully
serviceable instruments. When one trace is shifted
vertically across the entire screen, the position of the
other trace must not vary by more than 0.5mm.
A criterion in chopped operation is trace widening and
shadowing around and within the two traces in the upper
or lower region of the screen. Set TIME/DIV. switch to
2µs/div., depress the DUAL and CHOP. pushbutton, set
input coupling of both channels to GD and advance the
INTENS. control fully clockwise. Adjust FOCUS for a
sharp display. With the Y-POS. controls shift one of the
traces to a +2div., the other to a −2div. vertical position
from the horizontal center line of the graticule. Do not try
to synchronize (with the time variable control) the chop
frequency (0.5MHz)! Then alternately release and depress
theCHOP. pushbutton. Check for negligible trace widening
and periodic shadowing in the chopped mode.
It is important to note that in the I+II add mode (only ADD
depressed) or the I–II difference mode (INVERT CHII
button depressed in addition) the vertical position of the
trace can be adjusted by using both the Channel I and
Channel II Y-POS. controls.
In X-Y Operation (XY pushbutton depressed), the sensitivity
in both deflection directions will be the same. When the
signal from the built-in square-wave generator is applied to
the input of Channel II, then, as with Channel I in the vertical
direction, there must be a horizontal deflection of4div. when
the deflection coefficient is set to50mV/div. position (variable control set to its CAL. position, X-MAG. (x10) button in
out position). The check of the mono channel display with the
CHI/II button is unnecessary; it is contained indirectly in the
tests above stated.
Subject to change without notice
Triggering Checks
The internal trigger threshold is important as it determines
the display height from which a signal will be stably
displayed. It should be approx. 0.3-0.5div. for the HM303.
An increased trigger sensitivity creates the risk of response
to the noise level in the trigger circuit. This can produce
double-triggering with two out-of-phase traces.
Alteration of the trigger threshold is only possible internally.
Checks can be made with anysine-wave voltage between
50Hz and 1MHz. The AT/NORM. button should be in out
position (Automatic Triggering). Following this it should
be ascertained whether the same trigger sensitivity is also
present with Normal Triggering (AT/NORM. button
depressed). In this trigger mode, a LEVEL adjustment is
necessary. The checks should show the same trigger
threshold with the same frequency. On depressing the
SLOPE button, the start of the sweep changes from the
positive-going to the negative-going edge of the trigger
signal.
As described in the Operating Instructions, the trigger
frequency range is dependent on the trigger coupling
selected. For lower frequencies theLF coupling mode can
be selected. In this mode, triggering up to at least 1.5kHz
(sine-wave) is possible. Internally the HM303 should
trigger perfectly at a display height of approx. 0.5div.,
when the appropriate trigger coupling mode is set.
For external triggering (TRIG. EXT. button depressed),
the EXT. TRIG. input connector requires a signal voltage
of at least 0.3Vpp, which is in synchronism with the Y input
signal. The voltage value is dependent on the frequency
and the trigger coupling mode (AC-DC-LF).
Checking of the TV triggering is possible with a video
signal of any given polarity.
Use the TV position of the TRIG. switch for video sync
pulse separation. In TV triggering mode the TIME/DIV.
switch setting selects between line/horizontal pulse
separation (TIME/DIV. switch from .1ms/div. to .1µs/
div.) and frame/vertical pulse separation (TIME/DIV.
switch from .2s/div. to .2ms/div.). With the SLOPE
button the correct slope of the sync pulse (front edge)
must be selected. This slope is then valid for both sync
frequencies.
If both vertical inputs are AC coupled to the same signal
and both traces are brought to coincide exactly on the
screen, when working in the alternate dual channel
mode, then no change in display should be noticeable,
when the CH I/II - TRIG. I/II button is depressed or
released or when the TRIG. selector switch is changed
from AC to DC position.
Checking of the line/mains frequency triggering (50-60Hz)
is possible, when the input signal is time-related (multiple
or submultiple) to the power line frequency (TRIG. selector
switch to ~). There is no trigger threshold visible in this
trigger mode. Even very small input signals are triggered
stably (e.g. ripple voltage). For this check, use an input of
approx. 1V. The displayed signal height can then be varied
by turning the respective input attenuator switch and its
variable control.
Timebase
Before checking the timebase it should be ascertained
that the trace length is approx. 10div. in all time
ranges. If not, it can be corrected with the potentiometer
X x1 (see Adjusting Plan). This adjustment should be
made with the TIME/DIV. switch in a mid position (i.e.
20µs/div.). Prior to the commencement of any check set
the time variable control to CAL. The X-MAG. (x10)
button should be in out position. This condition should be
maintained until the variation ranges of these controls are
checked.
Check that the sweep runs from the left to the right
side of the screen (TIME/DIV. switch to 0.1s/div.; XPOS. control in mid-range). This check is only necessary
after changing the cathode-ray tube.
If a precise marker signal is not available for checking the
Timebase time coefficients, then an accurate sinewave generator may be used. Its frequency tolerance
should not be greater than ±.1%. The timebase accuracy
of the HM303 is given as ±3%, but it is considerably better
than this. For the simultaneous checking of timebase
linearity and accuracy at least 10 oscillations, i.e. 1 cycle
every div., should always be displayed. For precise
determination, set the peak of the first marker or cycle
peak exactly behind the first vertical graticule line using
the X-POS. control. Deviation tendencies can be noted
after some of the marker or cycle peaks.
Perfect TV triggering is achieved, when in both display
modes the amplitude of the complete TV signal (from
white level to the top of the line sync pulse) is limited
between 0.8 and 6div.
If a precise Time Mark Generator is used for checking,
Normal Triggering (AT/NORM. button depressed) and
LEVEL control adjustment is recommended.
The display should not shift horizontally during a change of
the trigger coupling from AC to DC with a sine-wave
signal without DC offset.
The following table shows which frequencies are required
for the particular ranges.
Subject to change without notice
T25
3
Component Tester
0.2
0.1
50
20
10
5
2
1
0.5
0.2
s/div.
s/div.
ms/div.
ms/div.
ms/div.
ms/div.
ms/div.
ms/div.
ms/div.
ms/div.
−
5 Hz
− 10 Hz
− 20 Hz
− 50 Hz
− 100 Hz
− 200 Hz
− 500 Hz
−
1 kHz
−
2 kHz
−
5 kHz
0.1
50
20
10
5
2
1
0.5
0.2
0.1
ms/div.
µs/div.
µs/div.
µs/div.
µs/div.
µs/div.
µs/div.
µs/div.
µs/div.
µs/div.
− 10kHz
− 20kHz
− 50kHz
− 100kHz
− 200kHz
− 500kHz
−
1MHz
−
2MHz
−
5MHz
− 10MHz
After pressing the COMP. TESTER button, a horizontal
straight line has to appear immediately, when the COMP.
TESTER socket is open. The length of this trace should be
approx. 8div. With connection of the COMP. TESTER
socket to the ground jack in the Y-Section, a vertical
straight line with approx. 6div. height should be displayed.
The above stated measurements have some tolerances.
Trace Alignment
When the X-MAG. (x10) button is depressed, a marker or
cycle peak will be displayed every 10div. ±5% (with
variable control in CAL. position; measurement in the
5µs/div. range). The tolerance is better measurable in the
50µs/div. range (one cycle every 1div.).
Holdoff time
The variation of the holdoff time during turning the HOLD
OFF knob can not be tested without opening the
instrument. However, a visual check can be made.
Without input signal, set TIME/DIV. and time variable
control cw, use automatic triggering. At the left hand stop
of the HOLDOFF knob, the trace should be bright. It
should darken remarkably at the right hand stop of the
HOLDOFF knob.
26
The CRT has an admissible angular deviation ±5° between
the X deflection plane D1-D2 and the horizontal center line
of the internal graticule. This deviation, due to tube
production tolerances (and only important after changing
the CRT), and also the influence of the earths magnetic
field, which is dependent on the instruments North
orientation, are corrected by means of the TR
potentiometer. In general, the trace rotation range is
asymmetric. It should be checked, whether the baseline
can be adjusted somewhat sloping to both sides round
about the horizontal center line of the graticule. With the
HM303 in its closed case, an angle of rotation ±0.57°
(0.1div. difference in elevation per 10div. graticule length)
is sufficient for the compensation of the earths magnetic
field.
Subject to change without notice
Service Instructions
General
The following instructions are intended as an aid for the
electronic technician, who is carrying out readjustments
on the HM303, if the nominal values do not meet the
specifications. These instructions primarily refer to those
faults, which were found after using the Test Instructions.
However, this work should only be carried out by properly
qualified personnel. For any further technical information
call or write to HAMEG. Addresses are provided at the
back of the manual. It is recommended to use only the
original packing material, should the instrument be shipped
to for service or repair (see also Warranty, page M2).
Instrument Case Removal
The rear cover can be taken off after unplugging the power
cords triple-contact connector and after two cross recessed
pan head screws (M4x30mm) with two washers on it
have been removed. While the instrument case is firmly
held, the entire chassis with its front panel can withdrawn
forward. When the chassis is inserted into the case later
on, it should be noticed that the case has to fit under the
flange of the front panel. The same applies for the rear of
the case, on which the rear cover is put.
Caution
During opening or closing of the case, the instrument
must be disconnected from all power sources for
maintenance work or a change of parts or
components. If a measurement, trouble-shooting, or
an adjustment is unavoidable, this work must be
done by a specialist, who is familiar with the risk
involved.
When the instrument is set into operation after the
case has been removed, attention must be paid to the
acceleration voltage for the CRT –2025V and to the
operating voltages for both final amplifier stages
185V and 141V. Potentials of these voltages are on
the PS-Board, the CRT-PCB, on the upper and lower
PCBs. Such potentials are moreover on the checkpoint
strips on the upper and lower horizontal PCBs. They
are highly dangerous and therefore precautions must
be taken. It should be noted furthermore that shorts
occuring on different points of the CRT high voltage
and unblanking circuitry will definitely damage some
semiconductors and the opto-coupler. For the same
reason it is very risky to connect capacitors to these
points while the instrument is on.
of the load is not impossible. Therefore, after switching
off, it is recommended to connect one by one all
terminals of the check strips on the upper PCB across
1kΩ to ground (chassis) for a period of 1 second.
Handling of the CRT needs utmost caution. The glass
bulb must not be allowed under any circumstances
to come into contact with hardened tools, nor should
it undergo local superheating (e.g. by soldering iron)
or local undercooling (e.g. by cryogenic-spray). We
recommend the wearing of safety goggles (implosion
danger).
The complete instrument (with case closed and POWER button depressed) is after each intervention
undergo a voltage test with 2200V, DC, between
accessible parts to both mains/line supply terminals.
This test is dangerous and requires an adequately
trained specialist.
Operating Voltages
All operating voltages (+6.3V, +12V, –12V, +141V, +185V,
–2025V) are stabilized by the switch mode power supply.
The +12V supply is further stabilized and used as a
reference voltage for –12V stabilisation. These different
operating voltages are fixed voltages, except the +12V,
which can be adjusted. The variation of the fixed voltages
greater than 5% from the nominal value indicates a fault.
Measurements of the high voltage may only be
accomplished by the use of a sufficient highly resistive
voltmeter (>10MΩ). You must make absolutely sure that
the electric strength of the voltmeter is sufficiently high.
It is recommended to check the ripple and also the
interaction from other possible sources. Excessive values
might be very often the reason for incomprehensible
faults.
Maximum and Minimum Brightness
Two variable resistors (220kΩ and 470kΩ), located on the
switch mode power supply PCB, are used for these
adjustment procedures (see Adjusting Plan). They may only
be touched by a properly insulating screwdriver (Caution!
High voltage!). The adjustments may possibly have to be
repeated, because the functions of both variable resistors
are dependent on each other. Correct adjustment is achieved,
when the trace can be blanked while XY pushbutton is
depressed and, in addition, when the requirement described
in the Test Instructions are met.
Astigmatism control
Capacitors in the instrument may still be charged,
even when the instrument is disconnected from all
voltage sources. Normally, the capacitors are
discharged approx. 6 seconds after switching off.
However, with a defective instrument an interruption
Subject to change without notice
The ratio of vertical and horizontal sharpness can be
adjusted by the variable resistor of 47kΩ, located on the
lower PCB (see Adjusting Plan). As a precaution however,
the voltage for the vertical deflecting plates (approx.
27
+85V) should firstly be checked, because this voltage will
affect the astigmastism correction. While the adjustment
is being carried out (with medium brightness and a 1MHz
square-wave signal), the upper horizontal square-wave
tops are firstly focussed with the FOCUS control. Then
the sharpness of the vertical lines are corrected with the
47kΩ Astigm. pot. The correction should be repeated
several times in this sequence. The adjustment is finished,
when the FOCUS knob exclusively brings no improvement of the sharpness in both directions.
Trigger Threshold
The internal trigger threshold should be in the range 0.3 to
0.5div. display height. It is strongly dependent on the
comparator IC. If there are compelling reasons to replace
this comparator, it may be that triggering becomes too
sensitive or too insensitive caused by the IC gain tolerances
(see Test Instructions: “Triggering Checks”, page T3). In
extreme cases, the 3.32kΩ hysteresis resistor of the
comparator should be changed. Generally, max. halving or
doubling of this resistance value should be sufficient. A
too small trigger threshold cause double-triggering or
premature trigger action due to interference pulses or
random noise. A too high trigger threshold prevents the
display of very small display heights.
adjacent circuit. Especially inspect the connections
between the PCBs, to front chassis parts, to CRT PCB, to
trace rotation coil (inside of CRTs shielding), and to the
control potentiometers and switches on top of and beneath
the PCBs. This visual inspection can lead to success much
more quickly than a systematic fault location using
measuring instruments. Prior to any extensive troubleshooting, also check the external power source.
If the instrument fails completely, the first and important
step − after checking the power fuses − will be to
measure the deflecting plate voltages of the CRT. In
almost any case, the faulty section can be located. The
sections represent:
1. Vertical deflection.
3. CRT circuit.
2. Horizontal deflection.
4. Power supply.
While the measurement takes place, the position controls of
both deflection devices must be in mid-position. When the
deflection devices are operating properly, the separate
voltages of each plate pair are almost equal then (Y approx.
80V and X approx 71V). If the separate voltages of a plate pair
are very different, the associated circuit must be faulty. An
absent trace in spite of correct plate voltages means a fault
in the CRT circuit. Missing deflection plate voltages is
probably caused by a defect in the power supply.
Trouble-Shooting the Instrument
Replacement of Components and Parts
For this job, at least an isolating variable mains/line
transformer (protection class II), a signal generator, an
adequate precise multimeter, and, if possible, an
oscilloscope are needed. This last item is required for
complex faults, which can be traced by the display of
signal or ripple voltages. As noted before, the regulated
high voltage and the supply voltages for the final stages
are highly dangerous. Therefore it is recommended to use
totally insulated extended probe tips, when troubleshooting the instrument. Accidental contact with
dangerous voltage potentials is then unlikely. Of course,
these instructions cannot thoroughly cover all kinds of
faults. Some common-sense will certainly be required,
when a complex fault has to be investigated.
For the replacement of parts and components use only
parts of the same or equivalent type. Resistors unspecified
in the diagrams have a power dissipation of 1/5 Watt
(Melf) or 1/8 Watt (Chip) respectively and a tolerance of
1%. Resistors in the high voltage circuit must have
sufficient electric strength. Capacitors without a voltage
value must be rated for an operating voltage of 63V. The
capacitance tolerance should not exceed 20%. Many
semiconductors are selected, especially all amplifier
transistors, which are contained in push-pull circuits. If a
selected semiconductor is defective, both push-pull
transistors of a stage should be replaced by selected
components, because otherwise there are possibly
deviations of the specified data or functions. The Service
Department can give you advice for troubleshooting and
replaceable parts. Replacement parts can be ordered by
letter or telephone from the nearest HAMEG Service
Office. Please supply the following information: Instrument type and serial number, description of the part (type
and part number on the circuit drawing).
If trouble is suspected, visually inspect the instrument
thoroughly after removal of the case. Look for loose or
badly contacted or discolored components (caused by
overheating). Check to see that all circuit board connections
are making good contact and are not shorting to an
28
Subject to change without notice
Short Instruction for HM303
Switching on and initial setting
Connect instrument to power outlet, depress red POWER button. LED indicates operating condition.
Case, chassis and all measuring terminals are connected to the safety earth conductor (Safety Class
I).
Do not depress any further button. TRIG. selector switch to AC.
AT/NORM. button released, CH.I input coupling switch to GD, set TIME/DIV. switch to 50µs/div.
Adjust INTENS. control for average brightness.
Center trace on screen using X-POS. and Y-POS.I controls. Then focus trace using FOCUS control.
Vertical amplifier mode
Channel I: All buttons in the Y section in out position.
Channel II: CHI/II button depressed.
Channel I and II: DUAL button depressed. Alternate channel switching: CHOP. (ADD) button in out position.
Signals <1kHz or time coefficient ≥1ms/div: DUAL and CHOP. buttons depressed.
Channel I+II or –I–II (sum): depress only ADD button.
Channel –I+II or +I–II (difference): depress ADD and the corresponding INVERT button.
Triggering mode
Select trigger mode with AT/NORM. button:
AT = Automatic Triggering <20Hz to 80MHz (out position). NORM. = Normal Triggering (depressed).
Trigger edge direction: select slope with SLOPE (±) button.
Internal triggering: select channel with TRIG. I/II (CH. I/II) button.
Alternating triggering (internal): ALT. pushbutton depressed, CHOP. button in the out position.
External triggering: TRIG. EXT. button depressed; sync signal (0.3Vpp to 3Vpp) to TRIG. INP. socket.
Line triggering: TRIG. selector switch to ~.
Select trigger coupling with TRIG. selector switch. Trigger frequency ranges:
AC: <20Hz to 100MHz; DC: DC to 100MHz; LF: DC to 1.5kHz.
TV: Composite video signal with line or horizontal frequency.
TIME/DIV. 0.2s/div. - 0.2ms/div. = field frequency
TIME/DIV. 0.1ms/div. - 0.1µs/div. = line frequency
Select edge direction with SLOPE (±) button (sync. pulse above +, below –).
Pay attention to trigger indicator: TR LED above the TRIG. selector switch.
Measurements
Apply test signal to the vertical input connectors of CH I and/or CH II.
Before use, calibrate attenuator probe with built-in square wave generator CAL.
Switch input coupling to AC or DC.
Adjust signal to desired display height with attenuator switch.
Select time coefficient on the TIME/DIV. switch.
Set trigger point with LEVEL knob for normal triggering.
Trigger complex or aperiodic signals with longer HOLD OFF-time.
Amplitude measurement with Y fine control at right stop (CAL.).
Time measurement with time fine control at right stop (CAL.).
Horizontal expansion 10 fold with X-MAG. (x10) button depressed.
External horizontal deflection (X-Y mode) with XY button depressed (X input: CH II).
Component Tester
Press COMP. TESTER button (on). Connect both component terminals to COMP. TESTER jacks.
In-circuit test: Circuit under test must be disconnected from battery or power (pull out power plug),
signals and ground (earth). Remove all signal connections to HM303 (cable, probe), then start testing.
Subject to change without notice
29
Front Panel Elements HM 303 (Brief Description
Element
Function
1
POWER
(pushbutton + LED)
Turns scope on and off.
LED indicates operating condition.
2
INTENS.
(knob)
3
- Front View)
Element
Function
21
.COMP. TESTER
(pushbutton switch)
Switch to convert oscilloscope
to component tester mode.
Intensity control
for trace brightness
22
Y-POS.I
(knob)
Controls vertical position
of channel I display.
TR
(potentiometer;
adjustment with
screwdriver)
Trace rotation.
To align trace with horizontal
graticule line. Compensates
influence of earth's magnetic field.
23
4
FOCUS
(knob)
Focus control for
trace sharpness.
−AC−
−DC
GD−
Selects input coupling of CH. I
(pushbutton switches) vertical amplifier.
DC = direct coupling
AC = coupling via capacitor
GD = signal disconnected
from input,
Y amplifier input grounded.
5
X-MAG. x10
(pushbutton switch)
10:1 expansion in the X direction.
Max. resolution 10ns/div.
24
INPUT CH I
(BNC connector)
Channel I signal input.
Input impedance 1MΩII20pF.
X-POS.
(knob)
Controls horizontal
position of trace.
25
INVERT CH I
(pushbutton switch)
HOLD OFF
(knob)
Controls holdoff-time
between sweeps.
Normal position = full ccw.
Inversion of CH. I display.
In combination with ADD button
= difference CH. II CH. I.
26
VOLTS/DIV.
(12 position
rotary switch)
Channel I input attenuator.
Selects Y input sensitivity
in mV/div. or V/div.
in 1-2-5 sequence.
27
VAR. GAIN
(knob)
Fine adjustment of Y amplitude CH. I.
Increases attenuation factor
min. by 2.5 (left hand stop).
For amplitude measurement must be
in CAL. position (right hand stop).
28
CH I/II-TRIG. I/II
(pushbutton switch)
No button depressed: CH. I only
and triggering from channel I.
When depressed, channel II only
and triggering from channel II.
(Trigger selection in DUAL mode).
6
7
8
9
XY
(pushbutton switch)
Selects X-Y operation,
stops sweep.
X signal via CH. II.
Attention! Phosphor burn-in without X signal.
TRIG.
(lever switch)
AC-DC-LF-TV-~
Trigger selector:
AC: 10Hz−100MHz.
DC: DC−100MHz.
LF: DC−1.5kHz.
TV: Triggering for frame and line.
~: Internal line triggering.
TR
(LED)
LED lights, if sweep is triggered.
10
ALT.
(pushbutton switch)
Triggering alternates between CHI and
CHII in alternating DUAL Channel mode
only.
29
Y MAG. x5
When depressed, increasing of
(pushbutton switches) Y-sensitivity (CH I or CHII resp.) 5 fold
(max. 1mV/div.)
11
−
SLOPE +/−
(pushbutton switch)
Selects the slope of the trigger signal.
+ = rising edge;
− = falling edge.
30
DUAL
(pushbutton
switch)
CHOP.
12
TIME/DIV.
(rotary switch)
Selects time coefficients (speeds)
of timebase,
from 0.2s/div. to 0.1µs/div.
Button released: one channel only.
Button depressed: channel I
and channel II in alternating mode.
DUAL and ADD buttons depressed:
CH. I and CH. II in chopped mode.
31
ADD
(pushbutton switch)
ADD depressed only: algebr. addition.
In combination with INVERT:
difference.
32
OVERSCAN
(LED indicators)
Direction indicators.
Illuminated when trace passes
vertical screen limits.
33
VAR. GAIN
(knob)
Fine adjustment of Y amplitude CH. II.
Increases attenuation factor
min. by 2.5 (left hand stop).
For amplitude measurement must be
in CAL. position (right hand stop).
34
VOLTS/DIV.
(12 position
rotary switch)
Channel II input attenuator.
Selects Y input sensitivity
in mV/div. or V/div.
in 1-2-5 sequence.
35
INVERT CH II
Inversion of CH. II display.
(pushbutton switch)
In combination with ADD button
= difference CH. I CH. II.
36
−DC−
−GD
AC−
Selects input coupling of the CH II
(pushbutton switches) vertical amplifier. Specs see
.
37
INPUT CH II
(BNC connector)
CH. II signal input and input for
horizontal deflection in X-Y mode.
38
Y-POS.II
(knob)
Controls vertical position
of channel II display.
Inoperative in X-Y mode.
Variable
timebase control
(center knob)
Variable adjustment of timebase.
Decreases X deflection speed
at least 2.5 fold.
For time measurements
turn to right hand stop.
14
TRIG. EXT.
(pushbutton switch)
Button released = internal triggering.
Button depressed = external triggering,
trigger signal via TRIG. INP 17 .
15
AT/NORM.
(pushbutton switch)
Button released = autom. triggering,
trace visible without input signal.
Button depressed = normal triggering
with LEVEL adjustment 16 .
13
16
LEVEL
(knob)
Adjustment of trigger level.
17
TRIG. INP.
(BNC connector)
Input for external trigger signal.
(Pushbutton TRIG. EXT. 14 depressed.)
18
CAL. 1kHz/1MHz
(pushbutton switch)
Selects calibrator frequency.
Button released: approx. 1kHz,
Button depressed: approx. 1MHz.
19
0.2V-2V
(test sockets)
Calibrator square wave output,
0,2Vpp or 2Vpp.
20
COMP. TESTER
(4mm jacks)
Connectors for test leads
of the Component tester.
2
4
3
1
6
5
8
7
12
10
9
11
16
14
13
Ω
18
19
20
21
22
24
23
15
17
Ω
25
27
26
28
30
29
35
33
31
32
34
37
36
38